[Enhancement] Support UTF8 Identifier

[syoyo]

TinyUSDZ now support UTF-8 Identifier by default in dev branch.

PixarAnimationStudios/OpenUSD#2120

https://openusd.org/release/api/_usd__page__u_t_f_8.html

• Basic UTF-8 processing
  • https://github.com/syoyo/tinyusdz/blob/dev/src/str-util.hh
• Support UTF-8 string in identifier(e.g. Prim name)
  • UTF8 Default Identifier validation support: de6b545
• UTF-8 support in isValidIdentifier https://github.com/syoyo/tinyusdz/blob/919fb30c4c34a5548ed2fcba058a262d81eb2a42/src/str-util.hh#L253
• MakeValidaIdentifier for UTF-8 Identifer?
• Support sorting UTF-8 string
• Provide utf8 normalization support?(if we do, use utf8proc.h https://github.com/JuliaStrings/utf8proc)
  • pxrUSD recommends to use NFC, but NFKC is preferred for multilingual environment. Thus TinyUSDZ would recommend NFKC for normalization.

[syoyo]

For efficient UTF8 processing...

Validating UTF-8 In Less Than One Instruction Per Byte
https://arxiv.org/abs/2010.03090

https://github.com/simdjson/simdjson

[syoyo]

For Identifier with UTF8, we need to follow Xid 31 rule

https://www.unicode.org/reports/tr31/

https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p1949r7.html

[syoyo]

Added initial UAX31 Default Identifier validation support in de6b545