Convert cedillas under D to commas

Convert cedillas under D to commas

According to Unicode 16.0.0 (chapter 7), U+0327 COMBINING CEDILLA is
ambiguous.  It can mean an actual cedilla, but it can also mean a
comma below.  This also applies to precomposed characters containing
it.  Unicode recommends default forms for various letters and in
particular says that for D and T (upper- and lower-case) the comma
form should be the default.

However, Unicode now has a separate U+021A LATIN CAPITAL LETTER T WITH
COMMA BELOW and recommends its use for Romanian.  So I think the
recommendation to render U+0162 LATIN CAPITAL LETTER T WITH CEDILLA with
a comma below is no longer applicable.

I have now updated Bedstead so that U+1E10 LATIN CAPITAL LETTER D WITH
CEDILLA is treated as having a comma below instead.  In practice, this
just means that it's unaffected by 'cv96'

All references to capital letters above apply equally to the
corresponding small letters.