This change implements the “is a descendant of a native host language
text alternative element” condition in the “F: Name From Content” step
at https://w3c.github.io/accname/#step2F in the “Accessible Name and
Description Computation” spec — to ensure that all descendant nodes get
included as expected in computations for accessible names for elements.
Otherwise, without this change, Ladybird unexpectedly skips descendant
element nodes when computing accessible names — which can result in the
wrong accessible name being returned.