Polish UI of inline-edits toolbar

[jrieken]

This pull request fixes the following issues:

• Fixes microsoft/vscode#226750

• Fixes microsoft/vscode-copilot#7628

• Fixes microsoft/vscode-copilot#7707

• Fixes (maybe) microsoft/vscode-copilot#7547

• Fixes microsoft/vscode#226966

The changes in this pull request include:

• Use lenses for accept/discard commands

• Use lens actions for headless inline UI (and not right-aligned button bar)

• Reveal inline chat when showing "save block" message

These changes improve the UI of the inline-edits toolbar and ensure that the inline chat is properly revealed when saving changes.