glocalfile: Add x-gvfs-notrash cache

The `g_unix_mount_get()` function is called each time when querying info,
or enumerating dirs.

It seems that it causes performance issues in some cases on some
platforms for certain `g_unix_mount_get()` implementations, see
!1707.

The `g_unix_mount_get call()` was introduced by the commit
4602a5ee and commit 4602a5ee, which are needed to set the
`access::can-trash` attribute now. Let's use the already existing mount
cache to improve the performance in this case.
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