Add Symbol.iterator functions for vscode.d.ts collection types (#151806)

* Add entries functions for vscode.d.ts collection types

Fixes #151802

* Spelling

* Enable lib.iterable in vscode.d.ts

* Switch to use `Symbol.iterator` instead of `entries`

* Use extends Iterable in more places

* Fixing testItemCollection types

* Fixing exthost testing

src/tsconfig.vscode-dts.json

@@ -14,6 +14,7 @@
 		"types": [],
 		"lib": [
 			"es5",
+			"ES2015.Iterable"
 		],
 	},
 	"include": [