Encodes a raw u32 value as UTF-8 into the byte buffer pointed to by dst.

Unlike char::encode_utf8, this method also handles codepoints in the surrogate range. (Creating a char in the surrogate range is UB.) The result is valid generalized UTF-8 but not valid UTF-8.

Safety

The behavior is undefined if the buffer pointed to by dst is not large enough to hold the encoded codepoint. A buffer of length four is large enough to encode any char.

For a safe version of this function, see the encode_utf8_raw function.