Update tests for unicode literals

test/libsolidity/syntaxTests/string/large_utf8_codepoint.sol

@@ -1,3 +1,4 @@
 contract C {
     string s = "\xf0\x9f\xa6\x84";
 }
+// ----

test/libsolidity/syntaxTests/string/string_ascii.sol

@@ -0,0 +1,9 @@
+contract test {
+    function f() public pure returns (string memory) {
+        return "hello world";
+    }
+    function g() public pure returns (string memory) {
+        return unicode"hello world";
+    }
+}
+// ----

test/libsolidity/syntaxTests/string/string_multipart_unicode.sol

@@ -0,0 +1,7 @@
+contract test {
+    function f() public pure returns (bytes32) {
+        bytes32 escapeCharacters = unicode"foo" unicode"😃, 😭, and 😈" unicode"!";
+        return escapeCharacters;
+    }
+}
+// ----

test/libsolidity/syntaxTests/string/string_multipart_unicode_mixed.sol

@@ -0,0 +1,8 @@
+contract test {
+    function f() public pure returns (bytes32) {
+        bytes32 escapeCharacters = "foo" hex"aa" unicode"😃, 😭, and 😈" "!" hex"00";
+        return escapeCharacters;
+    }
+}
+// ----
+// ParserError 2314: (106-113): Expected ';' but got 'HexStringLiteral'

test/libsolidity/syntaxTests/string/string_unicode.sol

@@ -1,7 +1,6 @@
 contract test {
     function f() public pure returns (string memory) {
-        return "😃, 😭, and 😈";
+        return unicode"😃, 😭, and 😈";
     }
 }
 // ----
-// ParserError 8936: (86-88): Invalid character in string.

test/libsolidity/syntaxTests/string/string_unicode_without_prefix.sol

@@ -0,0 +1,7 @@
+contract test {
+    function f() public pure returns (string memory) {
+        return "😃, 😭, and 😈";
+    }
+}
+// ----
+// ParserError 8936: (86-88): Invalid character in string.

test/libsolidity/syntaxTests/string/unicode_escape_literals.sol

@@ -19,3 +19,4 @@ contract test {
         return res;
     }
 }
+// ----