sql,tree: improve function resolution efficiency

[ajwerner]

sql: prevent allocations by avoiding some name pointers

We don't need pointers for these names. They generally won't escape.

sql,tree: change SearchPath to avoid allocations

The closure-oriented interface was forcing the closures and the variables they
referenced to escape to the heap. This change, while not beautiful, ends up being
much more efficient.

name                                         old time/op    new time/op    delta
SQL/MultinodeCockroach/Upsert/count=1000-16    20.4ms ±11%    18.9ms ± 8%   -7.47%  (p=0.000 n=20+19)

name                                         old alloc/op   new alloc/op   delta
SQL/MultinodeCockroach/Upsert/count=1000-16    10.1MB ±29%     9.8MB ±29%     ~     (p=0.231 n=20+20)

name                                         old allocs/op  new allocs/op  delta
SQL/MultinodeCockroach/Upsert/count=1000-16     56.3k ± 7%     50.2k ±10%  -10.81%  (p=0.000 n=19+19)

Release note: None

[cockroach-teamcity]

This change is 

[ajwerner]

See #85391 (comment)

[chengxiong-ruan]

many thanks!

[chengxiong-ruan]

Reviewable status: complete! 1 of 0 LGTMs obtained

[ajwerner]

TFTR!

bors r+

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[ajwerner]

#89335

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)