To simplify the interface of the Base32/Base64 encoding functions for raw data, this PR changes them from taking two arguments (pointer and length) to just one Span. Most calls to EncodeBase64 pass data from CDataStream instances, which unfortunately internally work with char* pointers rather than unsigned char*, but thanks to the recently introduced MakeUCharSpan helper, converting them is quite easy.
Backport of core PR19687.
Depends on D9183.