Rework RegExp engine and add support for proper unicode matching (#3746)

This change includes several bugfixes, general improvements, and support
for additional features.
- Added full support for web compatibility syntax defined in Annex B
- Implemented parsing and matching patterns in unicode mode
- Fixed capture results when iterating with nested capturing groups
- Significantly reduced regexp bytecode size
- Reduced stack usage during regexp execution
- Improved matching performance

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

tests/jerry/regexp-alternatives.js

@@ -58,3 +58,6 @@ assert (r.exec("a") == "a");
 
 r = new RegExp ("a|bb|c|d");
 assert (r.exec("b") == undefined);
+
+r = new RegExp("(?:a|b)\\b|\\.\\w+", "g");
+assert (r.exec("name.lower()")[0] === ".lower")