Introduce IO.new(..., path:) and promote File#path to IO#path.

[ioquatix]

The current semantics for File#path are at best difficult to deal with.

• Can raise an error.
• Makes it difficult for things that mock IO, e.g. GZip wrappers have to conditionally detect and add #path.

I've chosen to make this behave more like an attribute in IO#path which should ultimately be compatible with existing code except it can no longer raise an exception in normal usage.

https://bugs.ruby-lang.org/issues/19036

[headius]

Looks good to me but shouldn't rb_file_path remain as an alias for rb_io_path?

[headius]

Looks good to me but shouldn't rb_file_path remain as an alias for rb_io_path?

rb_file_path is not in any of the public header files, so it is not part of the public API and does not need to remain.

[ioquatix]

I'm going to merge this as is, but:

• Should we introduce IO#path=?
• Should we introduce IO#dup(..., path:)?