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/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/extractors/common/app-artifact-locator.ts

@@ -8,7 +8,7 @@ export async function findByFilePattern(
   pattern: string,
   directory: string,
   projectRootDir: string,
-): Promise<ArtifactLocation> {
+): Promise<ArtifactLocation | never> {
   if (!directory) { throw new Error('Missing directory'); }
   if (!pattern) { throw new Error('Missing file pattern'); }
 
@@ -42,5 +42,5 @@ function escapeRegExp(string: string) {
 }
 
 interface ArtifactLocation {
-  readonly absolutePath?: string;
+  readonly absolutePath: string;
 }

tests/checks/desktop-runtime-errors/check-desktop-runtime-errors/app/extractors/macos.ts

@@ -36,7 +36,10 @@ async function mountDmg(
     die(`Failed to mount DMG file at ${dmgFile}.\n${error}`);
   }
   const mountPathMatch = hdiutilOutput.match(/\/Volumes\/[^\n]+/);
-  const mountPath = mountPathMatch ? mountPathMatch[0] : null;
+  if (!mountPathMatch || mountPathMatch.length === 0) {
+    die(`Could not find mount path from \`hdiutil\` output:\n${hdiutilOutput}`);
+  }
+  const mountPath = mountPathMatch[0];
   return {
     mountPath,
   };
@@ -52,7 +55,10 @@ async function findMacAppExecutablePath(
     return die(`Failed to find executable path at mount path ${mountPath}\n${error}`);
   }
   const appFolder = findOutput.trim();
-  const appName = appFolder.split('/').pop().replace('.app', '');
+  const appName = appFolder.split('/').pop()?.replace('.app', '');
+  if (!appName) {
+    die(`Could not extract app path from \`find\` output: ${findOutput}`);
+  }
   const appPath = `${appFolder}/Contents/MacOS/${appName}`;
   if (await exists(appPath)) {
     log(`Application is located at ${appPath}`);