Don't rename file to backup file on save: instead copy it

[aster-void]

see helix-view/document.rs :959 for the code

it is causing too many issues:

• vite watch fails to detect changes
• inotifywatch fails to detect writes
• file perms change on save / see Writing changes file ownership #11988
• hard link breaks (even though it's explicitly checked??)

and it doesn't serve much purpose because:

• doesn't save disk space because the file is overwritten instantly
• we don't edit gigabytes of file very often

if the speed is critical on large files, move it only when the file is that large.