Enable Unicode support for RegEx class

Build PCRE2 thirdparty library with unicode support. RegEx objects
in Godot can now be used to recognize unicode strings.

(cherry picked from commit 9f10f6779cfdc15c1304c017bac5ad25de2383b6)

modules/regex/SCsub

@@ -7,7 +7,7 @@ env_regex = env_modules.Clone()
 
 if env["builtin_pcre2"]:
     thirdparty_dir = "#thirdparty/pcre2/src/"
-    thirdparty_flags = ["PCRE2_STATIC", "HAVE_CONFIG_H"]
+    thirdparty_flags = ["PCRE2_STATIC", "HAVE_CONFIG_H", "SUPPORT_UNICODE"]
 
     if env["builtin_pcre2_with_jit"]:
         thirdparty_flags.append("SUPPORT_JIT")