Add Persistent Buffers

This work is a heavily refactored and rewritten from TheForge's initial
code.

TheForge's original code had too many race conditions and was
fundamentally flawed as it was too easy to incur into those data races
by accident.

However they identified the proper places that needed changes, and the
idea was sound. I used their work as a blueprint to design this work.

This PR implements:

 - Introduction of UMA buffers used by a few buffers
(most notably the ones filled by _fill_instance_data).

Ironically this change seems to positively affect PC more than it does
on Mobile.

Updates D3D12 Memory Allocator to get GPU_UPLOAD heap support.

Metal implementation by Stuart Carnie.

Co-authored-by: Stuart Carnie <stuart.carnie@gmail.com>
Co-authored-by: TheForge team

servers/rendering/rendering_shader_container.h

@@ -57,6 +57,7 @@ protected:
 		uint32_t specialization_constants_count = 0;
 		uint32_t is_compute = 0;
 		uint32_t has_multiview = 0;
+		uint32_t has_dynamic_buffers = 0;
 		uint32_t compute_local_size[3] = {};
 		uint32_t set_count = 0;
 		uint32_t push_constant_size = 0;