Port `run-make/libtest-json` and `run-make/libtest-junit` to rmake Unlike #126773, this is just a straightforward port to `rmake`, without attempting to switch to compiletest or get rid of the (trivial) Python scripts. Part of #121876. r? ````@jieyouxu```` try-job: x86_64-msvc try-job: i686-mingw try-job: test-various try-job: aarch64-gnu try-job: aarch64-apple