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/Stubs/WindowVariablesStub.ts

@@ -6,30 +6,30 @@ import { SystemOperationsStub } from './SystemOperationsStub';
 import { LoggerStub } from './LoggerStub';
 
 export class WindowVariablesStub implements WindowVariables {
-  public system: ISystemOperations = new SystemOperationsStub();
+  public system?: ISystemOperations = new SystemOperationsStub();
 
-  public isDesktop = false;
+  public isDesktop? = false;
 
-  public os: OperatingSystem = OperatingSystem.BlackBerryOS;
+  public os?: OperatingSystem = OperatingSystem.BlackBerryOS;
 
-  public log: ILogger = new LoggerStub();
+  public log?: ILogger = new LoggerStub();
 
-  public withLog(log: ILogger): this {
+  public withLog(log?: ILogger): this {
     this.log = log;
     return this;
   }
 
-  public withIsDesktop(value: boolean): this {
+  public withIsDesktop(value?: boolean): this {
     this.isDesktop = value;
     return this;
   }
 
-  public withOs(value: OperatingSystem): this {
+  public withOs(value: OperatingSystem | undefined): this {
     this.os = value;
     return this;
   }
 
-  public withSystem(value: ISystemOperations): this {
+  public withSystem(value?: ISystemOperations): this {
     this.system = value;
     return this;
   }