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/ExpectDeepThrowsError.ts

@@ -0,0 +1,51 @@
+import { expect } from 'vitest';
+import { expectExists } from './ExpectExists';
+
+// `toThrowError` does not assert the error type (https://github.com/vitest-dev/vitest/blob/v0.34.2/docs/api/expect.md#tothrowerror)
+export function expectDeepThrowsError<T extends Error>(delegate: () => void, expected: T) {
+  // arrange
+  let actual: T | undefined;
+  // act
+  try {
+    delegate();
+  } catch (error) {
+    actual = error;
+  }
+  // assert
+  expectExists(actual);
+  expect(Boolean(actual.stack)).to.equal(true, 'Empty stack trace.');
+  expect(expected.message).to.equal(actual.message);
+  expect(expected.name).to.equal(actual.name);
+  expectDeepEqualsIgnoringUndefined(expected, actual);
+}
+
+function expectDeepEqualsIgnoringUndefined(
+  expected: object | undefined,
+  actual: object | undefined,
+) {
+  const actualClean = removeUndefinedProperties(actual);
+  const expectedClean = removeUndefinedProperties(expected);
+  expect(expectedClean).to.deep.equal(actualClean);
+}
+
+function removeUndefinedProperties(obj: object | undefined): object | undefined {
+  if (!obj) {
+    return obj;
+  }
+  return Object.keys(obj).reduce((acc, key) => {
+    const value = obj[key];
+    switch (typeof value) {
+      case 'object': {
+        const cleanValue = removeUndefinedProperties(value); // recurse
+        if (!cleanValue || !Object.keys(cleanValue).length) {
+          return { ...acc };
+        }
+        return { ...acc, [key]: cleanValue };
+      }
+      case 'undefined':
+        return { ...acc };
+      default:
+        return { ...acc, [key]: value };
+    }
+  }, {});
+}