Add tests showing hex literals are not allowed in Yul

test/libsolidity/syntaxTests/inlineAssembly/hex_assignment.sol

@@ -0,0 +1,9 @@
+contract C {
+  function f() public pure {
+    assembly {
+      let x := hex"0011"
+    }
+  }
+}
+// ----
+// ParserError 1856: (72-81): Literal or identifier expected.

test/libsolidity/syntaxTests/inlineAssembly/hex_expression.sol

@@ -0,0 +1,9 @@
+contract C {
+  function f() public pure {
+    assembly {
+      pop(hex"2233")
+    }
+  }
+}
+// ----
+// ParserError 1856: (67-76): Literal or identifier expected.

test/libsolidity/syntaxTests/inlineAssembly/hex_switch_case.sol

@@ -0,0 +1,11 @@
+contract C {
+  function f() public pure {
+    assembly {
+      switch codesize()
+      case hex"00" {}
+      case hex"1122" {}
+    }
+  }
+}
+// ----
+// ParserError 1856: (92-99): Literal or identifier expected.