Add border for dirty tabs (#59759)

* Theming for dirty tabs

* Improve border for dirty tabs
1. Make it thinner
2. Add a setting to disable it
3. Use 4 colors (activeFocused, activeUnfocused, inactiveFocused, inactiveUnfocused)
4. Move part of logic

* Hot apply of setting `dirtyTabBorder`

* Rename the setting

* Add default dirty border for all themes

* 3 of the 4 colors should be derived from the one main color

* Rename `dirty` to `modified`

* Rename `modifiedActiveFocusedBorder` to `modifiedBorder`

* Add modified border color for built-in themes

* More contrast

* Applying style directly on element

* Changing only color

* Using full border

* Using existing div for border styling

* Add setting to telemetry

* Uncomment cleanup code

* tweak colors and descriptions

* 💄

extensions/theme-abyss/themes/abyss-color-theme.json

@@ -372,6 +372,7 @@
 		"tab.border": "#2b2b4a",
 		// "tab.activeBackground": "",
 		"tab.inactiveBackground": "#10192c",
+		"tab.modifiedBorder": "#0072bf",
 		// "tab.activeForeground": "",
 		// "tab.inactiveForeground": "",