Add type().min/max for enums

test/libsolidity/semanticTests/enums/minmax.sol

@@ -0,0 +1,12 @@
+contract test {
+	enum MinMax { A, B, C, D }
+
+	function min() public returns(uint) { return uint(type(MinMax).min); }
+	function max() public returns(uint) { return uint(type(MinMax).max); }
+}
+
+// ====
+// compileViaYul: also
+// ----
+// min() -> 0
+// max() -> 3