nir: Get rid of nir_dest_bit_size()

nir: Get rid of nir_dest_bit_size()

We could add a nir_def_bit_size() helper but we use ->bit_size about 3x
as often as nir_dest_bit_size() today so that's a major Coccinelle
refactor anyway and this doesn't make it much worse.  Most of this
commit was generated byt the following semantic patch:

    @@
    expression D;
    @@

    <...
    -nir_dest_bit_size(D)
    +D.ssa.bit_size
    ...

Some manual fixup was needed, especially in cpp files where Coccinelle
tends to give up the moment it sees any interesting C++.

Acked-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24674>