Fix an issue of getExtBuiltins()

This function is used to import SPIR-V extended instruction set. It
mistakenly treated the name of SPIR-V extended instruction set as the
name of SPIR-V extension. For example, when we have such code

  getExtBuiltins("NonSemantic.DebugBreak")

'NonSemantic.DebugBreak' is added to SPIR-V extension. Rather, the
SPIR-V extension name should be 'SPV_KHR_non_semantics_info'. Therefore,
we must avoid this since the name of SPIR-V extended instruction set is
not necessarily equal to that of relevant SPIR-V extension. Adding a
SPIR-V extension must be done by calling addExtension() explicitly
outside this function.

This change also fixes disassembly issues of debugBreak().

gtests/Spv.FromFile.cpp

@@ -418,6 +418,7 @@ INSTANTIATE_TEST_SUITE_P(
         "spv.int64.frag",
         "spv.intcoopmat.comp",
         "spv.intOps.vert",
+        "spv.intrinsicsDebugBreak.frag",
         "spv.intrinsicsSpirvByReference.vert",
         "spv.intrinsicsSpirvDecorate.frag",
         "spv.intrinsicsSpirvDecorateId.comp",