Rename FormatableType to FormattableType

[breun]

I'm not a native English speaker, but I believe that if something can be formatted, then it is 'formattable' rather than 'formatable', so I believe the class name FormatableType should be renamed to FormattableType.

[odrotbohm]

Good catch! Unfortunately, I think this will have to wait until 2.0 as it's a public type and fixing the typo will break existing clients.

[breun]

Maybe FormattableType can already be introduced before 2.0 next to Formatabletype by letting FormattableType extend FormatableType and marking FormatableType as deprecated for removal in 2.0?

Then Spring Modulith itself could already switch to FormattableType and existing users can also already switch before 2.0 if they want.