ES31: Clean up Program::link This patch intends to solve some structure and coding style issues in Program::link to make it easier to support linking program with geometry shader. 1. Move all the shader specific validations to linkValidateShaders. Geometry shader related link validations can also be added here. 2. Rename functions with "VertexAndFragment" to "Graphics" because these functions will also be responsible for the validations on geometry shader. 3. Refer uniforms by pointer when validating uniforms. 4. Re-declare functions to 'static' if we can and capitialize the first letter of all static functions in Program.h. BUG=angleproject:1941 Change-Id: I46608e86bddc12d95cbbbf9a85803d07ccf843d8 Reviewed-on: https://chromium-review.googlesource.com/836149 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>