This CL is intended to move and factorize code only.

Move DisplayAndroid::generateConfigs to DisplayEGL::generateConfigs
because the code is generic and not Android specific. It will be
useful later to provide a default implementation of rx::DisplayEGL.
Same for createWindowSurface and createPbufferSurface, they have
been moved without changes from DisplayAndroid to DisplayEGL.

Unimplemented functions in DisplayOzone and DisplayAndroid have
been moved to DisplayEGL.

Bug: angleproject:4328
Change-Id: Ibbd36f99ea457cbd69391beb4a83f23403bc40fb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2038286
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>