Disable contributed openers by default in calls to openExternal

Fixes #114543

External and internal callers to openExternal may not expect (or want) their urls to be handled by a contributed opener. This change makes it so you have to explicitly enable using contributed openers when calling openExternal.

It also enables using contributed openers for a few places in our codebase

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

@@ -980,6 +980,7 @@ export interface MainThreadDebugServiceShape extends IDisposable {
 
 export interface IOpenUriOptions {
 	readonly allowTunneling?: boolean;
+	readonly allowContributedOpeners?: boolean | string;
 }
 
 export interface MainThreadWindowShape extends IDisposable {