Show draft comment icon in gutter when appropriate (#271536)

* Initial plan

* Add draft comment icon support in gutter and comments view

Co-authored-by: alexr00 <[email protected]>

* Add state property to Comment interface for draft support

Co-authored-by: alexr00 <[email protected]>

* Add color registration and CSS for draft comment glyph

Co-authored-by: alexr00 <[email protected]>

* clean up

* Fix known variables

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: alexr00 <[email protected]>