```
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.