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().

Test/baseResults/spv.intrinsicsDebugBreak.frag.out

@@ -0,0 +1,22 @@
+spv.intrinsicsDebugBreak.frag
+// Module Version 10000
+// Generated by (magic number): 8000b
+// Id's are bound by 8
+
+                              Capability Shader
+                              Extension  "SPV_KHR_non_semantic_info"
+               1:             ExtInstImport  "GLSL.std.450"
+               6:             ExtInstImport  "NonSemantic.DebugBreak"
+                              MemoryModel Logical GLSL450
+                              EntryPoint Fragment 4  "main"
+                              ExecutionMode 4 OriginUpperLeft
+                              Source GLSL 460
+                              SourceExtension  "GL_EXT_spirv_intrinsics"
+                              Name 4  "main"
+               2:             TypeVoid
+               3:             TypeFunction 2
+         4(main):           2 Function None 3
+               5:             Label
+               7:           2 ExtInst 6(NonSemantic.DebugBreak) 1(DebugBreak)
+                              Return
+                              FunctionEnd

Test/spv.intrinsicsDebugBreak.frag

@@ -0,0 +1,9 @@
+#version 460
+#extension GL_EXT_spirv_intrinsics : enable
+
+spirv_instruction (extensions = ["SPV_KHR_non_semantic_info"], set = "NonSemantic.DebugBreak", id = 1)
+void debugBreak();
+
+void main() {
+  debugBreak();
+}