- Added separate mutexes for both caches in the Blitter and used
  std::mutex instead of MutexLock.
- Removed some now unused inclusions/forward declaration from the
  Context class and fixed the fallout of doing that in other files.
- Also moved SwiftConfig to std::thread/std::mutex
- Removed unused inclusions of System/Thread.hpp where possible.

Bug b/132280877

Change-Id: Ic1a992ee3161c141ec1a16471420955c6309f58f
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31031Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>