Fix import path grammar and grammar testing details.

docs/grammar/SolidityLexer.g4

@@ -155,15 +155,20 @@ Not: '!';
 BitNot: '~';
 Inc: '++';
 Dec: '--';
+//@doc:inline
+DoubleQuote: '"';
+//@doc:inline
+SingleQuote: '\'';
 
 /**
- * A single quoted string literal restricted to printable characters.
- */
-StringLiteral: '"' DoubleQuotedStringCharacter* '"' | '\'' SingleQuotedStringCharacter* '\'';
-/**
- * A single non-empty quoted string literal.
+ * A non-empty quoted string literal restricted to printable characters.
  */
 NonEmptyStringLiteral: '"' DoubleQuotedStringCharacter+ '"' | '\'' SingleQuotedStringCharacter+ '\'';
+/**
+ * An empty string literal
+ */
+EmptyStringLiteral: '"' '"' | '\'' '\'';
+
 // Note that this will also be used for Yul string literals.
 //@doc:inline
 fragment DoubleQuotedStringCharacter: DoubleQuotedPrintable | EscapeSequence;
@@ -200,6 +205,7 @@ fragment DoubleQuotedUnicodeStringCharacter: ~["\r\n\\] | EscapeSequence;
 //@doc:inline
 fragment SingleQuotedUnicodeStringCharacter: ~['\r\n\\] | EscapeSequence;
 
+// Note that this will also be used for Yul hex string literals.
 /**
  * Hex strings need to consist of an even number of hex digits that may be grouped using underscores.
  */
@@ -315,6 +321,7 @@ YulDecimalNumber: '0' | ([1-9] [0-9]*);
 YulStringLiteral:
 	'"' DoubleQuotedStringCharacter* '"'
 	| '\'' SingleQuotedStringCharacter* '\'';
+//@doc:inline
 YulHexStringLiteral: HexString;
 
 YulWS: [ \t\r\n\u000C]+ -> skip ;