Migrate usages of ::_ToPath to use ::path instead

[sampersand]

This PR updates nearly all usages of string | _ToPath to just path, which are functionally identical.

Of note:

• Most of the changes are string | _ToPath, but a few of them were String | _ToPath. While this is functionally different, (path implies _ToStr), I verified that all the changed String | _ToPath do actually accept _ToStrs.
• FileUtils::path is now just an alias for the top-level ::path and is marked as deprecated.
• Find.find accepts String | _ToPath, but it's not quite right because Find.find also needs .dup, and some other things. Since I wanted this to be a simple PR, I didn't touch Find.find

[ksss]

👍