gl: Refactor image and command-context handling

- Move texture object code out of the monolithic header
- All texture binds go through the shared state
- Transient texture binds use a dedicated temp image slot shared with native UI

rpcs3/Emu/RSX/GL/glutils/common.cpp

@@ -0,0 +1,33 @@
+#pragma once
+#include "state_tracker.hpp"
+
+namespace gl
+{
+	static thread_local bool s_tls_primary_context_thread = false;
+	static gl::driver_state* s_current_state = nullptr;
+
+	void set_primary_context_thread(bool value)
+	{
+		s_tls_primary_context_thread = value;
+	}
+
+	bool is_primary_context_thread()
+	{
+		return s_tls_primary_context_thread;
+	}
+
+	void set_command_context(gl::command_context& ctx)
+	{
+		s_current_state = ctx.operator->();
+	}
+
+	void set_command_context(gl::driver_state& ctx)
+	{
+		s_current_state = &ctx;
+	}
+
+	gl::command_context get_command_context()
+	{
+		return { *s_current_state };
+	}
+}