x/build/cmd/golangbuild: update result_adapter to handle Go 1.24's go test -json output

[dmitshur]

Go 1.24 gained support for emitting build events in structured JSON on stdout, instead of the usual unstructured output on stderr (proposal #62067, release note).

This issue is a continuation of #70402 (comment), tracking the change needed on the LUCI side to be able to take advantage of this new feature.

CC @golang/release, @mknyszek.

[gabyhelp]

Related Code Changes

• cmd/go: re-enable build JSON from go test -json, now with GODEBUG

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[gopherbot]

Change https://go.dev/cl/634237 mentions this issue: main.star: extend gotestjsonbuildtext=1 to NEXT_GO

[dmitshur]

crrev.com/c/6174231 updates result_adapter with better support for Go 1.24 structured build events.
Edit: Also crrev.com/c/6179999 to fix handling of a common build failure affecting multiple packages.

After that's in, we can stop setting GODEBUG=gotestjsonbuildtext=1 in configuration.

[gopherbot]

Change https://go.dev/cl/642995 mentions this issue: main.star: stop setting GODEBUG=gotestjsonbuildtext=1 in x/build

[gopherbot]

Change https://go.dev/cl/642996 mentions this issue: main.star: stop setting GODEBUG=gotestjsonbuildtext=1 everywhere