[DO NOT MERGE] Pause compile just before compiling the fuzz target so that we can reuse it later.

[DonggeLiu]

@jonathanmetzman proposed a great idea about saving the machine state just before compiling the fuzz target so that we can compile different fuzz targets from that state later without having to go through the earlier commands.
This is particularly beneficial for OSS-Fuzz-Gen.

This PR is an (incomplete) PoC at that.
Ideally, we:

1. Replace the fuzz target compilation command and all commands after it with no-ops,
2. Save them into a script (e.g., $SRC/re-run.sh), and
3. Push the resulting image for later reuse.

In this way, we can reuse the image later by swapping the fuzz target source code and executing $SRC/re-run.sh.

The script in the PR can do 2, but not 1.
This might be OK already because steps in 1 are normally at the end, and there is unlikely any check to prevent them, but ideally, we should do 1, too.

To test this locally:

python infra/helper.py build_image libiec61850
docker run -ti --entrypoint=/bin/bash gcr.io/oss-fuzz/libiec61850
(in container) compile
cat /src/re-run.sh

[github-actions]

DonggeLiu has previously contributed to projects/libiec61850. The previous PR was #10109