Move quiche_feature_flags to actual file in Piper.

This breaks the dependency on all the genrule implementation details.

I've added a new test that will fail whenever a new QUICHE flag is
added, and prompt the CL author to update this file.

The update command as provided in the METADATA check is:
```
$ blaze build gfe/gfe2:quiche_feature_flags_list && cp blaze-genfiles/gfe/gfe2/quiche_feature_flags_list.h third_party/quiche/common/
```

I've confirmed that this leads to a significant reduction in the size of the envoy build dependency graph:

```
$ wc -l deps_envoy*
  # cl/
  25581 deps_envoy_2024-02.txt
  38946 deps_envoy_less-quiche.txt
  25337 deps_envoy_more-quiche.txt
```

As such, this eliminates around 98% of the additional transitive
dependencies introduced by cl/605634099.

PiperOrigin-RevId: 612458693
4 files changed
tree: ba42f01135a8d55aff0fd05aa7365c5c623af90b
  1. build/
  2. depstool/
  3. quiche/
  4. .bazelrc
  5. .bazelversion
  6. BUILD.bazel
  7. CONTRIBUTING.md
  8. LICENSE
  9. README.md
  10. WHITESPACE
  11. WORKSPACE.bazel
README.md

QUICHE

QUICHE stands for QUIC, Http, Etc. It is Google‘s production-ready implementation of QUIC, HTTP/2, HTTP/3, and related protocols and tools. It powers Google’s servers, Chromium, Envoy, and other projects. It is actively developed and maintained.

There are two public QUICHE repositories. Either one may be used by embedders, as they are automatically kept in sync:

To embed QUICHE in your project, platform APIs need to be implemented and build files need to be created. Note that it is on the QUICHE team's roadmap to include default implementation for all platform APIs and to open-source build files. In the meanwhile, take a look at open source embedders like Chromium and Envoy to get started:

To contribute to QUICHE, follow instructions at CONTRIBUTING.md.

QUICHE is only supported on little-endian platforms.