Use extension framework to enable #include directive.

This patch introduces a new extension, GL_GOOGLE_include_directive,
to enable support #include directives. It depends on the extension
GL_GOOGLE_cpp_style_line_directive.

Test/baseResults/preprocessor.include.disabled.vert.err

@@ -0,0 +1,13 @@
+ERROR: 0:8000: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8000: '#include' : must be followed by a file designation
+ERROR: 0:8001: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8001: '#include' : must be followed by a file designation
+ERROR: 0:8002: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8002: '#error' : unexpected include directive
+ERROR: 0:8003: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8003: '#include' : extra content after file designation
+ERROR: 0:8004: '#include' : required extension not requested: GL_GOOGLE_include_directive
+ERROR: 0:8004: '#error' : unexpected include directive
+ERROR: 10 compilation errors.  No code generated.
+
+

Test/preprocessor.include.disabled.vert

@@ -1,6 +1,7 @@
-#line 8000
-#include
-#include 123
-#include "foo"
-#include "foo" garbage
-#include "no-eol"
+#line 8000
+#include
+#include 123
+#include "foo"
+#include "foo" garbage
+#include "no-eol"
+

Test/preprocessor.include.enabled.vert

@@ -0,0 +1,7 @@
+#extension GL_GOOGLE_include_directive : enable
+#line 8000
+#include
+#include 123
+#include "foo"
+#include "foo" garbage
+#include "no-eol"

Test/test-preprocessor-list

@@ -4,7 +4,8 @@ preprocessor.edge_cases.vert
 preprocessor.errors.vert
 preprocessor.extensions.vert
 preprocessor.function_macro.vert
-preprocessor.include.vert
+preprocessor.include.enabled.vert
+preprocessor.include.disabled.vert
 preprocessor.line.vert
 preprocessor.line.frag
 preprocessor.pragma.vert