nir/algebraic: extend lowering patterns for conversions on smaller bit sizes

nir/algebraic: extend lowering patterns for conversions on smaller bit sizes

Conversions on smaller bit sizes should also be collapsed when composed.

This also adds more patterns on the
intS -> intB -> floatB ==> intS -> floatB
lowering so as to deal with any int size C > B instead of a fixed intB.

Closes: #7776
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Signed-off-by: Isabella Basso <isabellabdoamaral@usp.br>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20965>