Don't let m-x fill-paragraph break didchange

Don't let m-x fill-paragraph break didchange

M-x fill-paragraph represents some paragraph-fillling changes very
summarily.  Filling

    1 // foo
    2 bar

Into

    1 // foo bar

Only makes two changes: a deletion of the "// " and a replacement of a
newline with a space character.  The second change fooled Eglot's fix
for https://github.com/joaotavora/eglot/issues/259, by making a change similar to the one it is made to detect
and correct.  That fix should taget things that happen on the same
line, this not being one of those things.

* eglot.el (eglot--after-change): Only apply fix to https://github.com/joaotavora/eglot/issues/259 if
case-fiddling happens on same line.

GitHub-reference: fix https://github.com/joaotavora/eglot/issues/367