Migrate to pcre2 (HaxeFoundation#1037)

* Update pcre to pcre2-10.42

* Clean up

* Use generic pcre2 files

* Migrate regexp to pcre2

* Mark project/thirdparty as vendored

* Separate pcre2-8 and pcre2-16 into two groups

pcre2-8 and pcre2-16 can't be built together

* See if linux prefers the files in this order

* Fix regexp_matched error with unicode strings

* Add test for mixed unicode regex matching

See: HaxeFoundation/haxe#9500

* Fix length when converting utf16 regex to utf8

* Clean up whitespace in std tests

* Add outByteLength param to String::wc_str()

* Adjust parameter name

It is the length in code units, not in bytes

Author: tobil4sk

Diff for: .gitattributes

@@ -0,0 +1 @@
+project/thirdparty/*/** linguist-vendored

Diff for: include/hxString.h

@@ -166,7 +166,7 @@ class HXCPP_EXTERN_CLASS_ATTRIBUTES String
    inline const char *c_str() const { return utf8_str(); }
    inline const char *out_str(hx::IStringAlloc *inBuffer = 0) const { return utf8_str(inBuffer,false); }
    const wchar_t *wchar_str(hx::IStringAlloc *inBuffer = 0) const;
-   const char16_t *wc_str(hx::IStringAlloc *inBuffer = 0) const;
+   const char16_t *wc_str(hx::IStringAlloc *inBuffer = 0, int *outCharLength = 0) const;
 
    const char *__CStr() const { return utf8_str(); };
    const wchar_t *__WCStr() const { return wchar_str(0); }