opt: Add TrimCapabilities pass to spirv-opt tool (KhronosGroup#5545)

Add an option to the spirv-opt tool to run the TrimCapabilitiesPass.

Author: sudonatalie

source/opt/optimizer.cpp

@@ -623,6 +623,8 @@ bool Optimizer::RegisterPassFromFlag(const std::string& flag,
              pass_args.c_str());
       return false;
     }
+  } else if (pass_name == "trim-capabilities") {
+    RegisterPass(CreateTrimCapabilitiesPass());
   } else {
     Errorf(consumer(), nullptr, {},
            "Unknown flag '--%s'. Use --help for a list of valid flags",

tools/opt/opt.cpp

@@ -525,6 +525,10 @@ Options (in lexicographical order):)",
                USR/SYS time are returned by getrusage() and can have a small
                error.)");
   printf(R"(
+  --trim-capabilities
+               Remove unnecessary capabilities and extensions declared within the
+               module.)");
+  printf(R"(
   --upgrade-memory-model
                Upgrades the Logical GLSL450 memory model to Logical VulkanKHR.
                Transforms memory, image, atomic and barrier operations to conform