Rollup merge of #129037 - Zalathar:rmake-libtest, r=jieyouxu

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