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/presentation/components/Shared/Modal/Hooks/UseCurrentFocusToggle.ts

@@ -4,7 +4,7 @@ import { Ref, watchEffect } from 'vue';
  * Manages focus transitions, ensuring good usability and accessibility.
  */
 export function useCurrentFocusToggle(shouldDisableFocus: Ref<boolean>) {
-  let previouslyFocusedElement: HTMLElement | undefined;
+  let previouslyFocusedElement: HTMLElement | null;
 
   watchEffect(() => {
     if (shouldDisableFocus.value) {
@@ -17,7 +17,7 @@ export function useCurrentFocusToggle(shouldDisableFocus: Ref<boolean>) {
         return;
       }
       previouslyFocusedElement.focus();
-      previouslyFocusedElement = undefined;
+      previouslyFocusedElement = null;
     }
   });
 }