Standardize on the stricter Encode::encode("UTF-8", ...) everywhere
This is not only for code consistency, but also for consistency of output. Encode::encode_utf8(...) is equivalent to Encode::encode("utf8",...) which is the non-"strict" form of UTF-8. Strict UTF-8 encoding differs in that (from `perldoc Encode`): ...its range is much narrower (0 .. 0x10_FFFF to cover only 21 bits instead of 32 or 64 bits) and some sequences are not allowed, like those used in surrogate pairs, the 31 non-character code points 0xFDD0 .. 0xFDEF, the last two code points in any plane (0xXX_FFFE and 0xXX_FFFF), all non-shortest encodings, etc. RT deals with interchange with databases, email, and other systems. In dealing with encodings, it should ensure that it does not produce byte sequences that are invalid according to official Unicode standards.