[FIX] base_import_module: restore `<field file="...">` feature

Revision odoo/odoo@cabb9e7e573b86cd523980588360d8514090d370 introduced a
regression: This is no longer possible to import a data module
using `<field file="..."/>` in their data file.

This revision targets to restore the feature as expected.
The unit tests added covers the feature, so that regression
no longer happens in the future.

It introduces a new concept of temporary directory `file_open`
can read from.
e.g.
```py
with odoo.tools.file_open_temporary_directory(self.env) as module_dir:
   with zipfile.ZipFile('foo.zip', "r") as z:
      z.extract('foo/__manifest__.py', module_dir)
   with odoo.tools.file_open('foo/__manifest__.py', env=self.env) as f:
      manifest = f.read()
```

Note that `file_open` will be allowed to read from that temporary
directory only if `env` is passed to `file_open`,
and if the `env` is part of the same transaction/request than the `env`
passed to `file_open_temporary_directory`.

This is to avoid having users, whether from other databases,
or even the same database,
trying to access these directories not belonging to them.
e.g. If an admin uploads sensitive data in this temporary directory,
no one than him must be allowed to read from these files, not even
another user from his database.

closes odoo/odoo#126278

Signed-off-by: Denis Ledoux (dle) <dle@odoo.com>