zink: check for pending clears to determine write status of zs attachments

zink: check for pending clears to determine write status of zs attachments

as @Venemo discovered, zs layouts were being incorrectly set to readonly
in the case where the attachment was only used for an explicit clear,
so ensure that gets taken into account

cc: mesa-stable

fixes (radv):
dEQP-GLES31.functional.stencil_texturing.render.depth24_stencil8_clear
dEQP-GLES31.functional.stencil_texturing.render.depth32f_stencil8_clear

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17033>