Use Dawn's abseil build files when wgpu is enabled. To avoid building abseil with multiple different build files, use dawn's build files when it is available. Also use dawn's build files for out-of-chromium component builds to match dawn's conditions. Bug: angleproject:8555 Change-Id: I10c1578630dafa14fdd118feb66790eb0bf27792 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5371323 Commit-Queue: Geoff Lang <geofflang@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Liza Burakova <liza@chromium.org>