Replace UTF-8 decoder with branchless version by Christopher Wellons.
Decoding performance increase ranges from 30-40%.
Changes:
* Errors handling near the end of string changed. If input does not contain enough bytes, decoder returns `IM_UNICODE_CODEPOINT_INVALID`, consuming all remaining bytes while old decoder consumed only one byte.
Guarantees:
* At least one byte is consumed, if input had at least one byte available.
* Number of consumed bytes will never seek past end of string.
Requirements:
* `in_text` is a valid pointer.
* String pointed by `in_text` must be zero-terminated, or `in_text_end` is not NULL.
2 files changed
