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.

tests/unit/shared/ExceptionCollector.ts

@@ -0,0 +1,12 @@
+export function collectExceptionMessage(action: () => unknown): string {
+  let message: string | undefined;
+  try {
+    action();
+  } catch (e) {
+    message = e.message;
+  }
+  if (!message) {
+    throw new Error('action did not throw');
+  }
+  return message;
+}