Change runtime session icons

[dhruvisompura]

Follow up to #11905 and #12741 which added notebook sessions to the interpreter quick pick and the quarto icon to the console tab view.

We received feedback from folks that they didn't like:

1. the lack of color in the icons
2. the console icon being hard to read (known issue)
3. the lack of consistency in icon styles being introduced (codicons vs language-pack provided SVGs)

To try and address this we've landed on a middle ground: use the file icons that are used in the Explorer pane, breadcrumbs, etc. The file icon themes can be changed but the default one used is called Seti.

The downside to using file icons is that user can change the file icons and override what they see in the interpreter picker, console tab list, and session quick pick. The file icon theme can be changed by searching for "Preferences: File Icon Theme" (workbench.action.selectIconTheme) in the command palette and picking a different file icon theme. You can see that setting the file icon theme to Minimal or Disabled will override the icons we show.

The only time we show the language pack icons now is when you are selecting a runtime via a quickpick. If you're working with sessions, we use the file icon theme.

The positronQuarto codicon (codiconsLibrary.ts:763) has no remaining consumers after this PR. I'll remove the registration plus the glyph in a separate cleanup PR.

Screenshot

Release Notes

New Features

• Change icons shown for runtime sessions (Display notebook sessions in the select session quickpick #11905, Name unsaved Quarto file sessions with the file extension & include Quarto icon in session #12741)

Bug Fixes

• N/A

QA Notes

@:interpreter @:sessions @:console @:notebooks @:quarto @:top-action-bar

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical @:interpreter @:sessions @:console @:notebooks @:quarto @:top-action-bar

^{readme  valid tags}

[cindyytong]

lgtm! ty