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/application/Parser/Script/Compiler/Function/ISharedFunction.ts

@@ -4,15 +4,21 @@ import { FunctionCall } from './Call/FunctionCall';
 export interface ISharedFunction {
   readonly name: string;
   readonly parameters: IReadOnlyFunctionParameterCollection;
-  readonly body: ISharedFunctionBody;
+  readonly body: SharedFunctionBody;
 }
 
-export interface ISharedFunctionBody {
-  readonly type: FunctionBodyType;
-  readonly code: IFunctionCode | undefined;
-  readonly calls: readonly FunctionCall[] | undefined;
+export interface CallFunctionBody {
+  readonly type: FunctionBodyType.Calls,
+  readonly calls: readonly FunctionCall[],
 }
 
+export interface CodeFunctionBody {
+  readonly type: FunctionBodyType.Code;
+  readonly code: IFunctionCode,
+}
+
+export type SharedFunctionBody = CallFunctionBody | CodeFunctionBody;
+
 export enum FunctionBodyType {
   Code,
   Calls,