filename unescaping with non-ascii characters

bug: can't open files with non-ascii characters and whitespace in their names

related: none

code: input

touch 'fïle 1.txt'
cat fïle\ 1.txt

expect: the file contents

result: cat: 'fïle\ 1.txt': No such file or directory

version: df993477

context: using ion as a interactive shell, the escaping comes from tab-completion, using single quotes instead of \ works just fine.

behavior of bash/dash/zsh/fish/oil: open the file