Add curly brackets to excluded regexLexer chars (#4447)

* Adds curly brackets to excluded chars in regexLexer to allow for exact quantity clauses

Signed-off-by: Michael Han <han93008@gmail.com>

* add newline to example-exact-quantity.txt

---------

Signed-off-by: Michael Han <han93008@gmail.com>

Author: mlthan

xsd-regex/examples/example-exact-quantity.txt

@@ -0,0 +1 @@
+[a-z]{3}

xsd-regex/regexLexer.g4

@@ -49,7 +49,7 @@ PLUS        : '+';
 QUESTION    : '?';
 STAR        : '*';
 WildcardEsc : '.';
-Char        : ~('.' | '\\' | '?' | '*' | '+' | '(' | ')' | '|' | '[' | ']');
+Char        : ~('.' | '\\' | '?' | '*' | '+' | '(' | ')' | '|' | '[' | ']' | '{' | '}');
 
 // Quantifier's quantity rule support
 StartQuantity: '{' -> pushMode(QUANTITY);