general: Get the current process program id directly from the system

This allows us to avoid including KProcess' header file in files that only need to get the current process' program id.

src/core/core.h

@@ -297,6 +297,8 @@ public:
     /// Provides a constant reference to the speed limiter
     [[nodiscard]] const Core::SpeedLimiter& SpeedLimiter() const;
 
+    [[nodiscard]] u64 GetCurrentProcessProgramID() const;
+
     /// Gets the name of the current game
     [[nodiscard]] Loader::ResultStatus GetGameName(std::string& out) const;