Add support for typescript>4.4.0 (#18)

* Upgrade `ts-loader` to a version compatible with `typescript@4`

* Update tsconfig (base) for `typescript>4.4.0-dev`

`strictOptionalProperties` was renamed to `exactOptionalPropertyTypes`
in 4.4.0. See: microsoft/TypeScript#44626.

* Limit `typescript` to 4.6.x to support all bundled extensions

For example, `typescript-language-features` is not compatible with
4.7.x.

Author: randomir

extensions/tsconfig.base.json

@@ -6,7 +6,7 @@
 		],
 		"module": "commonjs",
 		"strict": true,
-		"strictOptionalProperties": false,
+		"exactOptionalPropertyTypes": false,
 		"useUnknownInCatchVariables": false,
 		"alwaysStrict": true,
 		"noImplicitAny": true,

package.json

@@ -196,9 +196,9 @@
     "source-map": "0.6.1",
     "source-map-support": "^0.3.2",
     "style-loader": "^1.0.0",
-    "ts-loader": "^6.2.1",
+    "ts-loader": "^8.0.0",
     "tsec": "0.1.4",
-    "typescript": "^4.4.0-dev.20210607",
+    "typescript": "~4.6.0",
     "typescript-formatter": "7.1.0",
     "underscore": "^1.12.1",
     "vinyl": "^2.0.0",