Use google/benchmark for performance tracking

In this patch we would vendor google/benchmark and break down the
benchmark into individual translation units, so that the benchmark
framework can apply filters on which benchmark code to run.

This patch vendors google/benchmark 1.9.4

Source: https://github.com/google/benchmark
Commit: eddb0241389718a23a42db6af5f0164b6e0139af

How to run the benchmark:

Benchmarks need to be built by passing in `-DBUILD_TESTING=ON` to CMake,
which is set by default.
To invoke the benchmarks, execute the `bssl_bench` binary.

You have the option to enumerate all of the benchmarks first by passing in
`--benchmark_list_tests`.
To run specific benchmarks, you may pass in `--benchmark_filter=$regex` where
`$regex` is an [`ECMAScript regular expression`](https://cppreference.com/w/cpp/regex/ecmascript.html).

You can specify a set of input sizes in bytes for relevant cipher suites
with the repeatable flag `-i` or `--input-size`.
You can let the benchmark run with a set of various thread counts with the
repeatable flag `-t` or `--threads`.
For more benchmark configuration options, you may read the manual by passing
in `--help` flag on launch.

Co-authored-by: Rudolf Polzer <rpolzer@google.com>
Bug: 383769319
Change-Id: Ic8d4cfd65065e61ae90c58bddb34463a5f398f14
Signed-off-by: Xiangfei Ding <xfding@google.com>
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/83327
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>