Standardize file naming and improve typings export

Renamed functions files to follow consistent camelCase convention. Added a missing type export for ITSInjex interface in the main index file, enabling better TypeScript type support and ensuring interfaces are available for external modules.

src/functions/register.ts

@@ -0,0 +1,35 @@
+import { TSInjex } from 'src/TSInjex';
+
+/**
+ * Register a dependency.
+ * @param identifier The identifier of the dependency.
+ * @param dependency The dependency to register.
+ */
+export function register<T>(identifier: string, dependency: T): void;
+
+/**
+ * Register a dependency.
+ * @param identifier The identifier of the dependency.
+ * @param dependency The dependency to register.
+ * @param deprecated A warning is logged when the dependency is resolved.
+ */
+export function register<T>(
+    identifier: string,
+    dependency: T,
+    deprecated?: true,
+): void;
+
+/**
+ * Register a dependency.
+ * @param identifier The identifier of the dependency.
+ * @param dependency The dependency to register.
+ * @param deprecated If true, the dependency is deprecated => a warning
+ * is logged when the dependency is resolved.
+ */
+export function register<T>(
+    identifier: string,
+    dependency: T,
+    deprecated?: boolean,
+): void {
+    TSInjex.getInstance().register(identifier, dependency, deprecated);
+}