Rework how we handle custom editors (#5696)

* update how we handle editors

* small edit

* handle changing languages

* implement generic language association

* implement notebook serializers

* fix tests

* formatting

* update how we handle editors

* small edit

* handle changing languages

* implement generic language association

* implement notebook serializers

* fix tests

* formatting

* fix broken

* fix compile

* fix tests

* add back in removed note book contributions

* fix layering

* fix compile errors

* fix workbench

* fix hanging promises

* idk why these changed

* fix change

* add comments to language change code

* fix a few bugs

* add query plan association

src/vs/workbench/common/editor.ts

@@ -447,8 +447,7 @@ export abstract class EditorInput extends Disposable implements IEditorInput {
 	 * Subclasses can set this to false if it does not make sense to split the editor input.
 	 */
 	supportsSplitEditor(): boolean {
-		// {{SQL CARBON EDIT}} @anthonydresser 05/19/2019 investigate
-		return false; // TODO reenable when multiple Angular components of the same type can be open simultaneously
+		return true;
 	}
 
 	/**
@@ -475,16 +474,6 @@ export abstract class EditorInput extends Disposable implements IEditorInput {
 
 		super.dispose();
 	}
-
-	// {{SQL CARBON EDIT}} @anthonydresser 05/19/2019 investigate
-	// Saving is not supported in the EditData query editor, so this can be overriden in its Input.
-	private _savingSupported: boolean = true;
-	public get savingSupported(): boolean {
-		return this._savingSupported;
-	}
-	public disableSaving() {
-		this._savingSupported = false;
-	}
 }
 
 export const enum ConfirmResult {