Fix up translation of `GetDimensions()`

Fixes #122

- In cases with an explicit mip level being specified, there was a mistake in how the argument for setting the mip level in the GLSL code was constructed that led to a parse error in GLSL

- Also, that argument is a `uint` in HLSL and an `int` in GLSL, so an explicit cast was needed

- The GLSL functions here seem to require a newer GLSL (at least higher than `420`), so I had to add in a capability for builtins to specify a required GLSL version. For now I made these ones require `450`.

- Added a test case to confirm that our lowering works (for some definition of "works")

1 files changed, 13 insertions, 0 deletions

diff --git a/source/slang/parser.cpp b/source/slang/parser.cpp
index 50205ff29..a624c58c5 100644
--- a/source/slang/parser.cpp
+++ b/source/slang/parser.cpp
@@ -729,6 +729,19 @@ namespace Slang
                 AddModifier(&modifierLink, modifier);
             }
 
+            else if (AdvanceIf(parser, "__glsl_version"))
+            {
+                auto modifier = new RequiredGLSLVersionModifier();
+                modifier->Position = loc;
+
+                parser->ReadToken(TokenType::LParent);
+                modifier->versionNumberToken = parser->ReadToken(TokenType::IntegerLiteral);
+                parser->ReadToken(TokenType::RParent);
+
+                AddModifier(&modifierLink, modifier);
+            }
+
+
             else if (AdvanceIf(parser, "layout"))
             {
                 parser->ReadToken(TokenType::LParent);