feat: inline AI suggestions inside code editors

[akshatbatra]

Closes #401

Functionality for inline AI suggestions inside code editors and dark mode support for AI Assistant.

Changes

• autocompletion.ts is the core that produces the suggestions.
• If the last LLM call is still being processed or if it's been less than 2 seconds since the last call, then another LLM call isn't made to make sure that LLMs are used conservatively and provide practical suggestions instead of intrusive completions one after the other.
• activityTracker.ts keeps track of timestamp of last user activity in the editors, this is used in autocompletion.ts to trigger the LLM call for inline suggestions if the user has been inactive for 1 second.
• Appropriate prompt has been added in prompts.ts to generate the suggestions.
• Auto-completion is registered before the editors mount.
• Inline AI suggestions can be enabled/disabled under advanced settings of AI Assistant configuration.
• AI Assistant, including the configuration popup, now supports dark mode via theming implementation.

Flags

• Some redundant code that applied concertoTheme has been removed as it was not having any effect anyway due to not being applied at the right place. No visual change can be observed due to the removal of that code. It was added at the right place to test but the color scheme of that theme didn't seem to go well with dark mode. Default theme (same as before) works well in both light and dark mode.
• This work was done with the old Playground UI as the base, it was later rebased onto restructuring/redesign branch to allow for testing with new design. When the redesign branch was merged, this branch was rebased onto main.

Demo Video

inline.completion.webm

Author Checklist

• Ensure you provide a DCO sign-off for your commits using the --signoff option of git commit.
• Vital features and changes captured in unit and/or integration tests
• Commits messages follow AP format
• Extend the documentation, if necessary
• Merging to main from fork:branchname

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