add support for multiple modulenames in extensions

[Flamefire]

This changes the allowed types of the modulename extension option:

• False to skip the sanity check and always install it when --skip is used
• str: Value for %(ext_name)s in the exts_filter template
• List of str: Multiple names to be used in the exts_filter template. All resulting commands must succeed.

This was previously suggested to allow Perl modules that are part of other Perl modules and hence don't need to be installed multiple times. See https://github.com/easybuilders/easybuild-easyconfigs/pull/12575

It replaces resolve_exts_filter_template by construct_exts_filter_cmds as the method now returns a, potentially empty, list which might cause errors if used without expecting a list.

The function is only used internally in framework and not by any easyblocks.

[boegel]

@Flamefire I changed to target branch in this PR from 5.0.x to develop, you should synchronize your PR branch with current develop branch (which has received a massive update after the release of EasyBuild v5.0.0, see #4825)

[Flamefire]

Rebased