Declaring stubs in directory

Right now, the <stubs> configuration node only supports the <file> node as a child.

This is problematic when:

• there are multiple files
• stubs files are generated dynamically

Having experienced both of the above, I think it would be nice if Psalm would support <directory> as <stubs>'s child node. Similar to how <projectFiles> already does.

Alternatively, the <file> node could support a pattern attribute to be used instead of <name>, so instead of

    <stubs>
        <file name="path/to/my/stubs/file1.php" />
        <file name="path/to/my/stubs/file2.php" />
        <file name="path/to/my/stubs/file3.php" />
        <file name="path/to/my/stubs/file4.php" />
    </stubs>

one could do either:

    <stubs>
        <directory name="path/to/my/stubs/" />
    </stubs>

or:

    <stubs>
        <file pattern="path/to/my/stubs/*.php" />
    </stubs>

Both approaches would solve this issue. The pattern attribute available for the StubsAttributeType XML type will enable it for any other usage of the <file> node in configuration.