Update Program[Pipeline]State to hold a ProgramExecutable Pointer This is a refactor CL to convert mExecutable in ProgramState and ProgramPipelineState to a pointer, so it can be changed to point to a different ProgramExecutable in a future CL. Bug: angleproject:4514 Test: end2end Change-Id: Id8ee9e5f2d1b02313973519cb2b4b0d5f7533b09 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2181447 Commit-Queue: Tim Van Patten <timvp@google.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>