Add a new TInterfaceBlock class member to hint ANGLE default Uniform In later change, we will transform floats in ANGLE default uniform struct from 32-bit to 16-bit in SPIRV. The new class member mIsDefaultUniformBlock will help us identify this special struct. This change is no op. Bug: angleproject:405795981 Change-Id: I939caf7491ab5d7de130ba6a2fd8b1202958c375 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6852398 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Commit-Queue: Yuxin Hu <yuxinhu@google.com>