Add SkReadPixelsRec.h & SkImage_Base.h to core.gni

This pebble's been in our shoe long enough!

The _Gpu.cpp files have also been moved into separate gpu.gni
file so they're gone.

Formatter also had its way with the file.

Change-Id: Ia9324953725f070c1a7b250bcb68311168560a29
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/373816
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
Auto-Submit: Adlai Holler <adlai@google.com>
1 file changed