Chore: create report translators lazily

[not-an-aardvark]

What is the purpose of this pull request? (put an "X" next to item)

[x] Other, please explain:

What changes did you make? (Give an overview)

This updates Linter#verify to only create a report translating function for a given rule after the rule has already reported a problem for a given file. When running ESLint on any given file, it's common for a vast majority of rules to not report any errors. This avoids creating an extra two functions in the common case, which has a significant effect on performance because creating ruleContexts is a hot path.

I tested the performance impact by running ESLint on its own codebase 5 times with and without this change applied, and taking the average time of the 5 runs in each case.

time bin/eslint.js 'tests/**/*.js' 'bin/**/*.js' 'lib/**/*.js' 'tools/**/*.js' 'conf/**/*.js' --rulesdir lib/internal-rules/ --ignore-pattern lib/linter.js

(I added lib/linter.js as an ignore pattern because this change modifies the contents of lib/linter.js, which could skew the results.)

Without this change applied, the average time was 15.11s. With this change applied, the average time was 14.66s, which is around a 3% end-to-end performance boost.

npm run perf reports no change in performance. I suspect this is because the npm run perf test includes an unusually large number of reported errors (see #9184)

Is there anything you'd like reviewers to focus on?

Nothing in particular

[eslintbot]

LGTM

[mention-bot]

@not-an-aardvark, thanks for your PR! By analyzing the history of the files in this pull request, we identified @nzakas, @gyandeeps and @mysticatea to be potential reviewers.

[eslintbot]

LGTM