Reworks GrGLGpu to track GL buffer state based on the unique
GrGpuResource ID. This eliminates the need to notify the gpu object
whenever a buffer is deleted.
This change also allows us to remove the type specifier from GrBuffer.
At this point a buffer is just a chunk of memory, and the type
given at creation time is just a suggestion to the GL backend about
which target to bind to for updates.
BUG=skia:
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Review URL: https://codereview.chromium.org/1854283004
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