Use ASCII chars in Content-Disposition filename parameter

Prior to this commit, gh-36328 avoided using RFC 2047 encoding for the
"filename" parameter and use ISO-8859-1 only. This change unfortunately
caused issues because some implementations might try and detect the
encoding automatically.

This commit restricts the filename parameter to ASCII encoding only by:
* transliterating characters to the closes ASCII character
("é"->"e", "ä"->"ae"...)
* falling back to "_" for other chacacters with non latin alphabet or
  emojis

Fixes gh-36805