b2 features for benchmarking are in separate module

[grisumbras]

This is so that the module could be easily imported in e.g. project-config.jam and then used for default build, custom build variants, etc.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.08%. Comparing base (37e3fd0) to head (2b9ad2a).

Additional details and impacted files

[](https://app.codecov.io/gh/boostorg/json/pull/992?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) ```diff @@ Coverage Diff @@ ## develop #992 +/- ## ======================================== Coverage 93.08% 93.08% ======================================== Files 87 87 Lines 8125 8125 ======================================== Hits 7563 7563 Misses 562 562 ``` ------ [Continue to review full report in Codecov by Sentry](https://app.codecov.io/gh/boostorg/json/pull/992?dropdown=coverage&src=pr&el=continue&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). > **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg) > `Δ = absolute (impact)`, `ø = not affected`, `? = missing data` > Powered by [Codecov](https://app.codecov.io/gh/boostorg/json/pull/992?dropdown=coverage&src=pr&el=footer&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Last update [37e3fd0...2b9ad2a](https://app.codecov.io/gh/boostorg/json/pull/992?dropdown=coverage&src=pr&el=lastupdated&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=boostorg).

[cppalliance-bot]

Benchmark test results. More info at https://benchmark.cppalliance.org/jsonbenchmarks-pullrequests/992/pullrequest.html