Rollup merge of #145253 - Kobzol:pr-check-2-doc-stage-1, r=jieyouxu

Document compiler and stdlib in stage1 in `pr-check-2` CI job

This restores the original behavior pre-#145011 (I thought that stage 2 makes more sense here, but it made the job ~30m slower, which is bad).

Let's see what will be the "new" duration, it should be ~55 minutes.

r? ```````@jieyouxu```````

Author: Zalathar

src/ci/docker/host-x86_64/pr-check-2/Dockerfile

@@ -33,11 +33,11 @@ ENV SCRIPT \
         python3 ../x.py test --stage 1 src/tools/compiletest && \
         python3 ../x.py doc bootstrap && \
         # Build both public and internal documentation.
-        RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc compiler --stage 2 && \
-        RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc library --stage 2 && \
+        RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc compiler --stage 1 && \
+        RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc library --stage 1 && \
         mkdir -p /checkout/obj/staging/doc && \
         cp -r build/x86_64-unknown-linux-gnu/doc /checkout/obj/staging && \
-        RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc library/test --stage 2 && \
+        RUSTDOCFLAGS=\"--document-private-items --document-hidden-items\" python3 ../x.py doc library/test --stage 1 && \
         # The BOOTSTRAP_TRACING flag is added to verify whether the
         # bootstrap process compiles successfully with this flag enabled.
         BOOTSTRAP_TRACING=1 python3 ../x.py --help