Refactor to enforce strictNullChecks

This commit applies `strictNullChecks` to the entire codebase to improve
maintainability and type safety. Key changes include:

- Remove some explicit null-checks where unnecessary.
- Add necessary null-checks.
- Refactor static factory functions for a more functional approach.
- Improve some test names and contexts for better debugging.
- Add unit tests for any additional logic introduced.
- Refactor `createPositionFromRegexFullMatch` to its own function as the
  logic is reused.
- Prefer `find` prefix on functions that may return `undefined` and
  `get` prefix for those that always return a value.

src/application/ApplicationFactory.ts

@@ -12,9 +12,6 @@ export class ApplicationFactory implements IApplicationFactory {
   private readonly getter: AsyncLazy<IApplication>;
 
   protected constructor(costlyGetter: ApplicationGetterType) {
-    if (!costlyGetter) {
-      throw new Error('missing getter');
-    }
     this.getter = new AsyncLazy<IApplication>(() => Promise.resolve(costlyGetter()));
   }