Vulkan: Adding custom pool allocator

Copied pool allocator used by compiler to common and hooking it up as
custom allocator for CommandPools. Modified it to support reallocation.

RendererVk now has a private poolAllocator and VkAllocationCallbacks
struct. The allocation callbacks are initialized to static functions
in RendererVk::initializeDevice() and then passed to CommandPool init()
and destroy() functions.

Using the pool allocator saves Command Pool/Buffer clean-up time which
was showing us as a bottleneck is some cases.

Bug: angleproject:2951
Change-Id: I81aa8a7ec60397676fa722d6435029db27947ef4
Reviewed-on: https://chromium-review.googlesource.com/c/1409867
Commit-Queue: Tobin Ehlis <tobine@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/tests/test_utils/ShaderCompileTreeTest.h b/src/tests/test_utils/ShaderCompileTreeTest.h
index a821351..9a2cd31 100644
--- a/src/tests/test_utils/ShaderCompileTreeTest.h
+++ b/src/tests/test_utils/ShaderCompileTreeTest.h
@@ -53,7 +53,7 @@
   private:
     TranslatorESSL *mTranslator;
 
-    TPoolAllocator mAllocator;
+    angle::PoolAllocator mAllocator;
 };
 
 // Returns true if the node is some kind of a zero node - either constructor or a constant union