This gets rid off the implicit dependency on `IsGlyphFullWidth`
for the IRM and DECSWL/DECDWL/DECDHL implementations.
## Validation Steps Performed
In pwsh:
* ``"`e[31mab`e[m`b`e[4h`e[32m$('*'*10)`e[m`e[4l"``
prints a red "a", 10 green "*" and a red "b" ✅
* ``"`e[31mab`e[m`b`e[4h`e[32m$('*'*1000)`e[m`e[4l"``
prints a red "a" and a couple lines of green "*" ✅
* ``"`e[31mf$('o'*70)`e[m`e#6`e#5"``
the right half of the row is erased ✅
Aside from overall simplifying `CharToColumnMapper` this fixes 2 bugs:
* The backward search loop may have iterated 1 column too far,
because it didn't stop at `*current <= *target`, but rather at
`*(current - 1) <= *target`. This issue was only apparent when
surrogate pairs were being used in a row.
* When the target offset is that of a trailing surrogate pair
the forward search loop may have iterated 1 column too far.
It's somewhat unlikely for this to happen since this code is
only used through ICU, but you never know.
This is a continuation of PR #16775.
