[BUGFIX] Respect '_language' argument for typoLink and LinkHandler

This patch fixes a bug where a t3 page URI with _language != 0
was resolved to a page in the default language. This caused
automatically generated redirects to translated pages to
redirect to the page in the default language.

We now use the same override handling for the '_language'
parameter (as already existed for 'L') when t3 page URIs are
resolved. Also, we ensure that both parameters are always removed
when the final URL is generated. Furthermore, this patch adds
tests to cover these cases.

Using the historical 'L' parameter still works and has been
added to be handled as language override.

Background information:

The '_language parameter' is the preferred parameter to
be used to specify the language in a t3 URI, not 'L'.

The behaviour of creating auto redirects on slug changes
was changed previously: The target was added as
LinkHandler URI (instead of the path). Along with this change,
the '_language' parameter was used to ensur...