RPC builds fail when PW_ENVIRONMENT_ROOT is set out of tree

[andy31415]

Default builds using .environment seem to be ok, however trying to build esp32-m5stack-all-clusters-rpc-ipv6only on the chip-build-vscode image fails with:

ninja: error: '../../../../config/esp32/third_party/pwenv/cipd/packages/pigweed/bin/protoc', needed by 'python/gen/third_party/connectedhomeip/third_party/pigweed/repo/third_party/nanopb/generate_nanopb_proto.pw_pystamp', missing and no known rule to make it

The reason seems to be that google/pigweed@ddbc9fc added support to use pw_env_setup_CIPD_PIGWEED to construct protoc paths and our build system seems to not really create these paths correctly for application builds.

The order of operations seems to be:

• pigweed bootstrap creates build_overrides/pigweed_environment.gni that contains pw_env_setup_CIPD_PIGWEED = "//../home/vscode/pigweed/env/cipd/packages/pigweed" (when running from /workspace with PW_ENVIRONMENT_ROOT set to /home/vscode/pigweed/env)
• example applications create a third_party/connectedhomeip subdirectory so that they can reference the SDK as //third_party/connectedhomeip
• https://github.com/project-chip/connectedhomeip/blob/master/examples/build_overrides/pigweed_environment.gni attempts to load the pigweed_environment.gni and adjust paths by prefixing //third_party/pigweed_environment

This may be ok when paths are within the root, as any paths will go through the symlink at thirtd_party/pigweed_environment. However this fails when relative paths are used.

[andy31415]

Re-open: the fix we have for m5stack does not work for other examples, where path is likely different. In particular efr32-brd4161a-lock-rpc-openthread_mtd compilation fails