Vulkan: Assert that attributes in shader info map are active
Vulkan: Assert that attributes in shader info map are active

Attributes that are not active shouldn't have made it to the
ShaderInterfaceVariableInfoMap of gl::ShaderType::Vertex.  This change
turns a few ifs to ASSERT in SpirvVertexAttributeAliasingTransformer.

Bug: angleproject:4249
Change-Id: I3da4ea773eae20fe2f126b82f7790e9f2cab0bc1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2491929
Reviewed-by: Charlie Lao <2661ca4ca24c371418789adbc76dfb4875087223@google.com>
Reviewed-by: Tim Van Patten <c7814369a8d3d5671c484acc7b3215f1bf4221be@google.com>
Commit-Queue: Shahbaz Youssefi <582eeec4f08a2ccd61e3ef52115e6e7c571582de@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle