Allow hex string literals in Yul.

docs/grammar/Solidity.g4

@@ -564,5 +564,5 @@ yulPath: YulIdentifier (YulPeriod YulIdentifier)*;
  */
 yulFunctionCall: (YulIdentifier | YulEVMBuiltin) YulLParen (yulExpression (YulComma yulExpression)*)? YulRParen;
 yulBoolean: YulTrue | YulFalse;
-yulLiteral: YulDecimalNumber | YulStringLiteral | YulHexNumber | yulBoolean;
+yulLiteral: YulDecimalNumber | YulStringLiteral | YulHexNumber | yulBoolean | YulHexStringLiteral;
 yulExpression: yulPath | yulFunctionCall | yulLiteral;

docs/grammar/SolidityLexer.g4

@@ -263,6 +263,7 @@ YulLeave: 'leave';
 YulLet: 'let';
 YulSwitch: 'switch';
 YulTrue: 'true';
+YulHex: 'hex';
 
 /**
  * Builtin functions in the EVM Yul dialect.
@@ -314,7 +315,7 @@ YulDecimalNumber: '0' | ([1-9] [0-9]*);
 YulStringLiteral:
 	'"' DoubleQuotedStringCharacter* '"'
 	| '\'' SingleQuotedStringCharacter* '\'';
-
+YulHexStringLiteral: HexString;
 
 YulWS: [ \t\r\n\u000C]+ -> skip ;
 YulCOMMENT: '/*' .*? '*/' -> channel(HIDDEN) ;

docs/yul.rst

@@ -174,7 +174,10 @@ whitespace, i.e. there is no terminating ``;`` or newline required.
 Literals
 --------
 
-You can use integer constants in decimal or hexadecimal notation.
+As literals, you can use integer constants in decimal or hexadecimal notation
+or strings as ASCII (`"abc"`) or HEX strings (`hex"616263"`) of up to
+32 bytes length.
+
 When compiling for the EVM, this will be translated into an
 appropriate ``PUSHi`` instruction. In the following example,
 ``3`` and ``2`` are added resulting in 5 and then the