Vulkan: Don't detach separable shaders in Program::detachShader() To support Program Pipeline Objects, we need to hold on to the shaders in separable programs, rather than detaching them during glDetachShader()/glCreateShaderProgramv(). This is necessary due to requiring the shader information for validating shader interfaces, varyings, etc. Instead, a new ShaderMap of bools will be stored in ProgramState::mAttachedShadersMarkedForDetach to track when a caller attempts to detach a shader from a separable Program. Later, when a new shader is attached, we will first validate that the old shader is marked to be detached, and if so, release it then. Bug: angleproject:3570 Change-Id: I63fac2e5914c1c1a73f0b37863bac0f185ecb44c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2084399 Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Commit-Queue: Tim Van Patten <timvp@google.com>