Embed sh::ShaderVariable data member into gl::LinkedUniform ProgramExecutable::load and save function is load/save each individual data members. Uniform can be quite large as shown in some app traces and this causes performance problem even when program memory has a cache hit. This CL flattens gl::LinkedUniform structure by embedding sh::ShaderVariable data members so that we can remove unrelated members and also prepare for further optimization in future CLs. Bug: b/275102061 Change-Id: I7c18cb73e359fba7cd6375b4b1635e9040ef140d Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4735152 Reviewed-by: Roman Lavrov <romanl@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Charlie Lao <cclao@google.com>