Prototyping custom editors (#77789)

* Custom Editor exploration

For #77131

Adds a prototype of custom editors contributed by extensions. This change does the following:

- Introduces a new contribution point for the declarative parts of a custom editor
- Adds API for registering a webview editor provider. This lets VS Code decided when to create a webview editor
- Adds an `openWith` command that lets you select which editor to use to open a resource from the file explorer
- Adds a setting that lets you say that you always want to use a custom editor for a given file extension
- Hooks up auto opening of a custom editor when opening a file from quick open or explorer
- Adds a new extension that contributes a custom image preview for png and jpg files

Still needs a lot of UX work and testing. We are also going to explore a more generic "open handler" based approach for supporting custom editors

Revert

* Re-use existing custom editor if one is already open

* Don't re-create custom editor webview when clicking on already visible custom editor

* Move customEditorInput to own file

* First draft of serializing custom editor inputs

* Use glob patterns instead of simple file extensions for matching custom resoruces for custom editors

* Add descriptions

* Try opening standard editor while prompting for custom editor

* Make sure we hide image status on dispose

* Make sure we restore editor group too

* Use glob patterns for workbench.editor.custom

* Allow users to configure custom editors for additional file types

* Use filename glob instead of glob on full resource path

* Adding placeholder for prompt open with

* Add enableByDefault setting for editor contributions

* Enable custom editors by default and add `discretion` enum

Changes `enableByDefault` boolean to a `discretion` enum. This should give more flexibility if we want other options (such as forcing a given custom editor to always be used even if there are other default ones)

* Allow custom editors to specify both a scheme and filenamePattern they are active for

* Rework custom editor setting

* Don't allow custom editors to be enabled for all resources by a config mistake

* Replace built-in image editor with one from extension

* Adding reopen with command

* Improve comment

* Remove commented code

* Localize package.json and remove image

* Remove extra lib setting from tsconfig

src/vs/workbench/api/common/extHost.api.impl.ts

@@ -523,6 +523,10 @@ export function createApiFactoryAndRegisterActors(accessor: ServicesAccessor): I
 			registerWebviewPanelSerializer: (viewType: string, serializer: vscode.WebviewPanelSerializer) => {
 				return extHostWebviews.registerWebviewPanelSerializer(viewType, serializer);
 			},
+			registerWebviewEditorProvider: (viewType: string, provider: vscode.WebviewEditorProvider) => {
+				checkProposedApiEnabled(extension);
+				return extHostWebviews.registerWebviewEditorProvider(viewType, provider);
+			},
 			registerDecorationProvider(provider: vscode.DecorationProvider) {
 				checkProposedApiEnabled(extension);
 				return extHostDecorations.registerDecorationProvider(provider, extension.identifier);