Problem:
Directories that are "trusted" by `vim.secure.read()`, are not detectable later
(they will prompt again). https://github.com/neovim/neovim/discussions/33587#discussioncomment-12925887
Solution:
`vim.secure.read()` returns `true` if the user trusts a directory.
Also fix other bugs:
- If `f:read('*a')` returns `nil`, we treat that as a successful read of
the file, and hash it. `f:read` returns `nil` for directories, but
it's also documented as returning `nil` "if it cannot read data with the
specified format". I reworked the implementation so we explicitly
treat directories differently. Rather than hashing `nil` to put in the
trust database, we now put "directory" in there explicitly*.
- `vim.secure.trust` (used by `:trust`) didn't actually work for
directories, as it would blindly read the contents of a netrw buffer
and hash it. Now it uses the same codepath as `vim.secure.read`, and
as a result, works correctly for directories.
272dba7f07