internal/shader: add test files

Updates #2011

internal/shader/testdata/issue2011.expected.vs

@@ -0,0 +1,12 @@
+void F0(out float l0);
+void F1(out int l0);
+
+void F0(out float l0) {
+	l0 = 1.0;
+	return;
+}
+
+void F1(out int l0) {
+	l0 = 2;
+	return;
+}

internal/shader/testdata/issue2011.go

@@ -0,0 +1,13 @@
+package main
+
+const F = float(1)
+
+func Foo() float {
+	return F
+}
+
+const I = int(2.0)
+
+func Bar() int {
+	return I
+}