#48258

supporting viewpanecontainer in panels with PaneCompositePanel and ViewContainerLocation

fixes #48258

Part of microsoft/vscode-remote-release#1777

Adopt it for untitled and text file models. Use it for indicating dirty count in explorer and document edited on macOS.

- Import aliasing symbol in file
- Missing function calls in conditional
- Missing return statement

Part of #78168

These events should not be mutated by listeners

Emitters should generally not be reassigned as their corresponding event would also be lost. Marking these as readonly just to enforce this

fixes #79742