HLSL: Add string basic type and recognize string declaration grammar.

This includes the "< decl ; decl ; >" syntax which has its own namespace.
This functionality is not implemented, just silently accepted.

Test/baseResults/hlsl.string.frag.out

@@ -0,0 +1,64 @@
+hlsl.string.frag
+Shader version: 450
+gl_FragCoord origin is upper left
+0:? Sequence
+0:10  Function Definition: main(f1; (global float)
+0:10    Function Parameters: 
+0:10      'f' (layout(location=0 ) in float)
+0:?     Sequence
+0:11      Sequence
+0:11        move second child to first child (temp float)
+0:?           '@entryPointOutput' (layout(location=0 ) out float)
+0:11          'f' (layout(location=0 ) in float)
+0:11        Branch: Return
+0:?   Linker Objects
+0:?     '@entryPointOutput' (layout(location=0 ) out float)
+0:?     'f' (layout(location=0 ) in float)
+
+
+Linked fragment stage:
+
+
+Shader version: 450
+gl_FragCoord origin is upper left
+0:? Sequence
+0:10  Function Definition: main(f1; (global float)
+0:10    Function Parameters: 
+0:10      'f' (layout(location=0 ) in float)
+0:?     Sequence
+0:11      Sequence
+0:11        move second child to first child (temp float)
+0:?           '@entryPointOutput' (layout(location=0 ) out float)
+0:11          'f' (layout(location=0 ) in float)
+0:11        Branch: Return
+0:?   Linker Objects
+0:?     '@entryPointOutput' (layout(location=0 ) out float)
+0:?     'f' (layout(location=0 ) in float)
+
+// Module Version 10000
+// Generated by (magic number): 80001
+// Id's are bound by 13
+
+                              Capability Shader
+               1:             ExtInstImport  "GLSL.std.450"
+                              MemoryModel Logical GLSL450
+                              EntryPoint Fragment 4  "main" 8 10
+                              ExecutionMode 4 OriginUpperLeft
+                              Name 4  "main"
+                              Name 8  "@entryPointOutput"
+                              Name 10  "f"
+                              Decorate 8(@entryPointOutput) Location 0
+                              Decorate 10(f) Location 0
+               2:             TypeVoid
+               3:             TypeFunction 2
+               6:             TypeFloat 32
+               7:             TypePointer Output 6(float)
+8(@entryPointOutput):      7(ptr) Variable Output
+               9:             TypePointer Input 6(float)
+           10(f):      9(ptr) Variable Input
+         4(main):           2 Function None 3
+               5:             Label
+              11:    6(float) Load 10(f)
+                              Store 8(@entryPointOutput) 11
+                              Return
+                              FunctionEnd

Test/hlsl.string.frag

@@ -0,0 +1,12 @@
+string s = "string1";
+string e = "";
+string bracket < string a = "nested" ; > ; 
+string brackets < string b = "nest1" ; string c = "nest2" ; string d = "nest3" ; > ;
+string brackete1 <  > ;
+string brackete2 < ; > ;
+string brackete3 < ; ; > ;
+
+float main(float f)
+{
+    return f;
+}