This removes an unnecessary string creation/clone for
get_lang_for_layout.
get_lang_for_layout is only read by match_element_lang which creates an
AtomString. Directly returning an AtomString from the returned &str is
more efficient than creating a String in between.
Testing: The output is exactly the same, so no need for extra tests.
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Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>