pkg/query: Add fast map of strings to json marshaling

[brancz]

This has a ~82% improvement compared to the previously used method.

$ benchstat stdlib.txt ours.txt
name        old time/op  new time/op  delta
MarshalMap   412ns ± 1%    73ns ± 0%  -82.34%  (p=0.008 n=5+5)

Which results in an overall improvement of ~44% for real life profiling data that has labels:

$ benchstat old.txt new.txt
name                old time/op  new time/op  delta
ArrowFlamegraph-10   289ms ± 1%   161ms ± 1%  -44.23%  (p=0.008 n=5+5)

Let's profile live stream where we explored this: https://www.youtube.com/watch?v=4hZtHsOWKKk (turns out we incorrectly measured and the improvement was actually significantly larger than initially thought)

[alwaysmeticulous]

🤖 Meticulous replayed 50 user sessions and took 326 screenshots. Meticulous has not yet run on 2d6b35a of the main branch and so there was nothing to compare against.

If you recently setup Meticulous, this is expected. Meticulous will start reporting comparisons for new pull requests after the next commit to the main branch.

_{Last updated for commit 356bc4d. This comment will update as new commits are pushed.}

[metalmatze]

Very cool! I knew this was eventually going to happen, but didn't expect it so soon 😃
Very happy that we are not using reflection anymore now!