feat: Automatically start in Insert mode for specific schemes

[astron8t-voyagerx]

What this PR does / why we need it:

This PR adds a new configuration option vim.startInInsertModeSchemes that allows users to specify document URI schemes that should automatically start in Insert mode.

Use Cases

• GitHub PR Comments: Comment editors use the comment scheme. Users typically want to immediately start typing without pressing i first.
• Jupyter Notebooks: Notebook cells use the vscode-notebook-cell scheme. This provides a better experience when editing cells.
• GitLens commit messages: Uses the gitlens scheme.

Configuration Example

{
"vim.startInInsertModeSchemes": ["comment", "vscode-notebook-cell"]
}

Implementation Details

• When a new editor is created with a matching URI scheme, it starts in Insert mode
• When focus changes to an existing editor with a matching scheme, it automatically switches to Insert mode
• The existing startInInsertMode setting is preserved and works alongside this new feature

Which issue(s) this PR fixes

This PR partially addresses #8782 by providing a flexible way for users to customize Vim behavior for specific contexts like Jupyter notebooks and comment editors.

While #8782 requested the ability to disable Vim for certain contexts, this PR takes a complementary approach: instead of disabling Vim entirely, it allows automatically entering Insert mode for specific URI schemes. This provides a better UX for contexts where users primarily want to type text (comments, notebook cells, etc.) while still maintaining Vim functionality when needed.

Special notes for your reviewer:

• The implementation uses editor.document.uri.scheme which is a stable VS Code API
• Default value is an empty array [], so existing users are not affected
• I've also updated test/testConfiguration.ts to include the new property
• I've run yarn test

[J-Fields]

Thanks!