Add rename to std.fs API

[squeek502]

Closes#6344

• Moves fs.rename functions to fs.renameAbsolute to match other functions outside of fs.Dir
• Adds fs.Dir.rename that takes two paths relative to the given Dir
• Adds fs.rename that takes two separate Dir's that the given paths are relative to (for renaming across directories without having to make the second path relative to a single directory)
• Fixes FileNotFound error return in std.os.windows.MoveFileExW
• Returns error.RenameAcrossMountPoints from renameatW
  • Matches the RenameAcrossMountPoints error return in renameatWasi/renameatZ

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Notes:

• There is likely a better name or API for Dir.renameAt. I couldn't really come up with anything, though (renameElsewhere? renameTransfer? renameTo?).

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The tests are currently failing on Windows. EDIT: Split the Windows rename failure to its own issue: #6364

• On Windows, the implementation of both renameAbsolute and Dir.rename do not allow renaming directories.
  • renameAbsoluteuses MOVEFILE_REPLACE_EXISTING which "cannot be used if lpNewFileName or lpExistingFileName names a directory."
  • Dir.renameuses OpenFile which fails with error.IsDir

[squeek502]

Made the directory rename tests get skipped on Windows for now, the fix there ended up being much more complex than anticipated so I split it into its own issue: #6364

[andrewrk]

There is likely a better name or API for Dir.renameAt. I couldn't really come up with anything, though (renameElsewhere? renameTransfer? renameTo?).

How about std.fs.rename (2 dir arguments) vs std.fs.Dir.rename (1 dir argument) ?

[andrewrk]

Nice work! I have 1 requested change, and 1 optional suggestion for naming, and then this is good to go.

[squeek502]

Done + squashed.

One other implementation I thought of, but it might be somewhat messy (especially with the Z/W variants), would be to have only Dir.rename and then have it take a struct as the new path with the Dir being optional:

struct {
dir: ?Dir=null,
path: []constu8,
}

Usage:

dir.rename("old_file", .{ .path="new_file" });
dir.rename("old_file", .{ .dir=other_dir, .path="new_file" });

(if dir is not given for the new path, then it uses self for both)

[andrewrk]

nice work!

[andrewrk]

One other implementation I thought of

I'm not against that but I would personally prefer the differently named functions for this case.

Thanks for this PR, std.fs just got much cleaner!