Remove deprecated Intel GPA from General optimization tips

Intel's Graphics Performance Analyzer has been deprecated and
no longer receives support. Microsoft's PIX can generally supersede
it nowadays, although it's exclusive to Direct3D 12.

This also adds links to more tools like Xcode and Special K
(the latter of which works with Direct3D 12 at least in Godot).

Author: Calinou

tutorials/performance/general_optimization.rst

@@ -60,11 +60,13 @@ There are several methods of measuring performance, including:
 - Using external GPU profilers/debuggers such as
   `NVIDIA Nsight Graphics <https://developer.nvidia.com/nsight-graphics>`__,
   `Radeon GPU Profiler <https://gpuopen.com/rgp/>`__,
-  `Intel Graphics Performance Analyzers <https://www.intel.com/content/www/us/en/developer/tools/graphics-performance-analyzers/overview.html>`__, or
+  `PIX <https://devblogs.microsoft.com/pix/download/>`__ (Direct3D 12 only),
+  `Xcode <https://developer.apple.com/documentation/xcode/optimizing-gpu-performance>`__ (Metal only), or
   `Arm Performance Studio <https://developer.arm.com/Tools%20and%20Software/Arm%20Performance%20Studio>`__.
 - Checking the frame rate (with V-Sync disabled). Third-party utilities such as
-  `RivaTuner Statistics Server <https://www.guru3d.com/files-details/rtss-rivatuner-statistics-server-download.html>`__
-  (Windows) or `MangoHud <https://github.com/flightlessmango/MangoHud>`__
+  `RivaTuner Statistics Server <https://www.guru3d.com/files-details/rtss-rivatuner-statistics-server-download.html>`__ (Windows),
+  `Special K <https://www.special-k.info/>`__ (Windows),
+  or `MangoHud <https://github.com/flightlessmango/MangoHud>`__
   (Linux) can also be useful here.
 - Using an unofficial `debug menu add-on <https://github.com/godot-extended-libraries/godot-debug-menu>`__.