Turbopack: widen the chunk ident hash from 7 to 10 base38 chars
7 base38 chars (~36 bits nominal, ~32 effective) makes chunk-name collisions
a birthday problem for large apps: ~10^5 chunks sharing a name prefix collide
with probability of order 1, and next build aborts with 'Two or more assets
with different content were emitted to the same output path'.
Fixes the failure reported in #97765 (deterministic repro) and #96976.
Co-authored-by: jonnyuniverse <jon@fractionalventure.partners>
Co-authored-by: Tobias Koppers <1365881+sokra@users.noreply.github.com>