Don't rely on the current default (which is 2048 bytes) buffer size for
blocks -- which ends up being too small for most shaders. Since we
already rely on value_id_bound to allocate an array of vtn_value, use
that to estimate a better value.
In addition to space for the array, we approximate the extra size of
extra data structures with the size of vtn_ssa_value, and skip it to the
next size (double it) to cover the CFG related allocations. This
results in only single system allocation necessary to back the temporary
data for the majority of the shaders.
Parsing code was slightly reordered so we can validate and read the
value_id_bound before the temporary allocator is created.
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25279>