fix(snowflake): manually construct quantile calls with WITHIN GROUP

[gforsyth]

The Snowflake SQLGlot dialect rewrites calls to percentile_cont to
include WITHIN GROUP (ORDER BY ...)
as per https://docs.snowflake.com/en/sql-reference/functions/percentile_cont
using the rule add_within_group_for_percentiles

If we have copy=False set in our call to compile, if there is more
than one quantile, the rewrite rule fails on the second pass because
of some mutation in the first pass. To avoid this error, we create the
expression with the within group included already and skip the (now
unneeded) rewrite rule.

Fixes #8768

[gforsyth]

Snowflake tests are good, some funky formatting where I removed a few socket error messages

🐚 just test snowflake
bringing up nodes...
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