Show highlighted symbol in the scrollbar

[fxsalazar]

Release Notes:

• Added highlighted symbols to the scrollbar; partially mentioned in:
  • https://github.com/zed-industries/zed/issues/5308
  • https://github.com/zed-industries/zed/issues/4866

[cla-bot[bot]]

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[fxsalazar]

@cla-bot check

[cla-bot[bot]]

The cla-bot has been summoned, and re-checked this pull request!

[mikayla-maki]

Thank you!