[PHP-wasm] File mounting in NODEFS (#2338)

## Motivation for the change, related issues

We accidentally added support for mounting files to the Playground CLI
by creating a directory with the file path and mounting the file into
that node.

This PR removes the accidental mount implementation and adds file
mounting support to `createNodeFsMountHandler` by detecting the mount
type and creating the correct node type (symlink, file, directory).

Because Emscripten allows only the mounting of directories, we had to
remove the directory check from `FS.mount` during PHP-wasm compile time.

To ensure mounting works as expected for files, directories, and
symlinks, this PR also adds mount tests that include file system
operations like reading files, modifying files, deleting, moving, and
unmounting.

While writing tests I found two bugs and addressed them in this PR:

- When attempting to remove a mountpoint node `FSHelpers.rmdir` would
first remove all files and directories from the mountpoint and fail to
remove the mountpoint in the end. To address this, we now detect if a
directory we are attempting to delete is a mount point and throw an
error early. The same applies for moving a mount point.
- `FSHelpers.copyRecursive` copied files and directories, but skipped
symlinks. Now the function will also copy symlinks.

## Testing Instructions (or ideally a Blueprint)

- CI

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Co-authored-by: Brandon Payton <[email protected]>

Author: bgrgicak