compiler: add support for type parameters (aka generics)

...that was surprisingly easy.

compiler/compiler_go118.go

@@ -0,0 +1,18 @@
+//go:build go1.18
+// +build go1.18
+
+package compiler
+
+// Workaround for Go 1.17 support. Should be removed once we drop Go 1.17
+// support.
+
+import "go/types"
+
+func init() {
+	typeParamUnderlyingType = func(t types.Type) types.Type {
+		if t, ok := t.(*types.TypeParam); ok {
+			return t.Underlying()
+		}
+		return t
+	}
+}