rr::Config holds the full reactor configuration state.
rr::Config::Edit holds edits on a config, which can be applied on top of the current defaults.

Default configurations are updated atomically, preventing modifications to the default state from tearing.

Bug: b/137167988
Change-Id: Ib05f2cfc31ab22fb9a891a267fffe33c18691028
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/33768
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>