[cherry-pick] sessions: Add inline remote management actions - #344266

Cherry-pick of #344228 from main.

Summary

Bring the Remote Environments editor closer to the Environment picker's Manage action picker:

• Add inline Copy Address to every remote row, including offline and busy rows. Copy the connection address, not the display name, without connecting.
• Add inline Change Preferred Agent Location to SSH and tunnel rows. Reuse the existing prompt, preference storage, reconnect, cancellation, and notification behavior. SSH preferences use the stable host identity rather than a forwarded port, including when no provider is currently available. Disable this action during an existing connection or management operation.
• Add inline Update Server for incompatible hosts advertising an upgrade method. Reuse the existing progress, restart delay, reconnect, and notification flow; revalidate the capability on invocation, prevent duplicate requests, and restore keyboard focus when the action disappears.
• Add inline Delete for supported tunnel rows, including discovered/offline tunnels. Share the confirmation dialog with the Tunnels picker and delete the service-side registration through the existing service, not the local Remove action. Protect the tunnel currently hosted by this application, revalidate after confirmation, retain rows on failure, and prevent stale discovery from restoring a deleted row.
• Prefer fresh tunnel discovery metadata over cached records and stale provider labels in Remotes, while preserving explicit local display-name overrides.
• Preserve keyboard navigation, focus restoration, and shared toolbar hover behavior; update accessibility help and add regression tests and four-theme action fixtures.

Created from freshly pulled main at ff05b50d4ef; this is not stacked on the previous Remotes PR.

Related functional test plan: #344161.

Remaining Manage-action parity gaps

These are reported, not implemented in this PR:

• Remove Remote for removable non-environment hosts. This is distinct from the Environment and tunnel rows' service-side Delete operations.
• Exact per-row Open Settings / Open SSH Configuration access. Section-level configuration actions cover much of this, but do not reproduce every host-specific route (notably WSL and explicit-credential SSH).

WebSocket hosts remain outside this editor and retain their existing Manage route.

Validation

Passed:

• npm run gulp compile-client - initial client compilation and type-check, zero errors.
• npm run typecheck-client - final client type-check including confirmed tunnel deletion, passed.
• npm run build-fast -- --client-only - refreshed client output after the final test and fixture changes.
• The following Electron selection - 245 passing:

.\scripts\test.bat --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remotesModel.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remotesWidget.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remoteHostOptions.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remoteAgentHostActions.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\electron-browser\remotesEditor.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\electron-browser\tunnelAgentHostServiceImpl.test.ts --reporter dot

• Browser tests - 389 passing across WebKit and Edge:

npm run test-browser-no-install -- --browser webkit --browser chromium-msedge --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remotesModel.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remotesWidget.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remoteHostOptions.test.ts --run src\vs\sessions\contrib\providers\remoteAgentHost\test\browser\remoteAgentHostActions.test.ts --reporter dot

• Changed-file ESLint and hygiene - 10 files passed; git diff --check passed. Commands were run before committing:

$files = @(git diff --name-only -- '*.ts')
npm run eslint -- $files
node build\hygiene.ts $files
git diff --check

• Component Explorer: all 64 Remotes fixtures rendered and disposed without errors. Inspected the initial inline actions in all four themes and the final six-action layout in Dark and Light High Contrast.
• Browser keyboard check reached all six tunnel actions and verified they fit without clipping. Tests verify confirmation/cancellation, duplicate protection, backend failure, post-confirmation state changes, stale discovery, and focus restoration after deletion.

Automated validation did not delete real tunnels or perform a live server upgrade. Clipboard values, preference persistence, cancellation, missing-provider behavior, reconnect failures, duplicate actions, advertised upgrade methods, restart delays, stale capabilities, and error notifications are covered by tests. The maintainer exercised live upgrades and identified separate existing startup-timeout/duplicate-supervisor and reconnect-target issues; those are not fixed by this PR. Custom-hover display could not be verified in the isolated fixture; the actions use the existing shared toolbar hover delegate unchanged.

Manual checks

• Open Remote Environments and copy an SSH, tunnel, WSL, and offline Environment address.
• On SSH and tunnels, cancel Change Preferred Agent Location and confirm no preference or connection change.
• Choose either preferred location and confirm it is saved and the host reconnects; verify a reconnect failure is reported without losing the preference.
• Confirm Update Server appears only for incompatible hosts advertising an upgrade method; verify progress, restart/reconnect, and failures on a suitable test host.
• Cancel Delete on a test tunnel and confirm it remains; confirm deletion and verify its service-side registration and local row are removed.
• Confirm a tunnel hosted by this application cannot be deleted until hosting stops.
• Reach the new actions using the keyboard; confirm Copy Address remains available during a pending connection or update.