Consolidate GPU buffer implementations

Consolidates all the different buffer implementations into a single
GrBuffer class. This will allow us to add new buffer types, use DSA in
OpenGL, track buffer bindings by unique ID, cache buffers without
respect to the type of data they have been used for previously, etc.
This change is strictly a refactor; it introduces no change in
functionality.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1825393002

Committed: https://skia.googlesource.com/skia/+/8b1bff29675afd25843439eade634a57f68fe16f

Review URL: https://codereview.chromium.org/1825393002
diff --git a/src/gpu/vk/GrVkCaps.cpp b/src/gpu/vk/GrVkCaps.cpp
index 3126ca0..6d1d844 100644
--- a/src/gpu/vk/GrVkCaps.cpp
+++ b/src/gpu/vk/GrVkCaps.cpp
@@ -30,7 +30,7 @@
     fUseDrawInsteadOfClear = false; //TODO: figure this out
 
     fMapBufferFlags = kNone_MapFlags; //TODO: figure this out
-    fGeometryBufferMapThreshold = SK_MaxS32;  //TODO: figure this out
+    fBufferMapThreshold = SK_MaxS32;  //TODO: figure this out
 
     fMaxRenderTargetSize = 4096; // minimum required by spec
     fMaxTextureSize = 4096; // minimum required by spec
@@ -110,7 +110,7 @@
 
     // Assuming since we will always map in the end to upload the data we might as well just map
     // from the get go. There is no hard data to suggest this is faster or slower.
-    fGeometryBufferMapThreshold = 0;
+    fBufferMapThreshold = 0;
 
     fMapBufferFlags = kCanMap_MapFlag | kSubset_MapFlag;