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/shared/Assertions/ExpectExists.ts

@@ -0,0 +1,14 @@
+/**
+ * Asserts that the provided value is neither null nor undefined.
+ *
+ * This function is a more explicit alternative to `expect(value).to.exist` in test cases.
+ * It is particularly useful in situations where TypeScript's control flow analysis
+ * does not recognize standard assertions, ensuring that `value` is treated as
+ * non-nullable in the subsequent code. This can prevent potential type errors
+ * and enhance code safety and clarity.
+ */
+export function expectExists<T>(value: T): asserts value is NonNullable<T> {
+  if (value === null || value === undefined) {
+    throw new Error('Expected value to exist');
+  }
+}