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-backreference.js

@@ -24,3 +24,6 @@ assert (r == undefined);
 r = new RegExp ("(a)*b\\1").exec("b");
 assert (r[0] == "b");
 assert (r[1] == undefined);
+
+assert (JSON.stringify (/[[]?(a)\1/.exec("aa")) === '["aa","a"]');
+assert (JSON.stringify (/\1{2,5}()\B/.exec("asd")) === '["",""]');