Simplify Gson setup

[Marcono1234]

Tries to simplify the Gson setup as described in #6742 (comment).

I cannot easily verify that this works because I am using Windows, therefore I have marked this pull request as draft.

[Marcono1234]

Could also alternatively run Maven for the parent project and only build the gson module as described in https://stackoverflow.com/a/3899772, though this approach here works as well.
Do you prefer one solution over the other?

[DavidKorczynski]

From the CI:

/src/gson/gson/src/test/java/com/google/gson/internal/LinkedTreeMapTest.java:[164,20] Invalid java.lang.SafeVarargs annotation. Instance method <T>assertIterationOrder(java.lang.Iterable<T>,T...) is not final.

It looks like you're running into the same issue as I described here #6742 (comment)

[Marcono1234]

You are right sorry. Should be fixed now. Can you please run the CI workflows again?

[Marcono1234]

The build is now failing because for execution of ProGuard (which is part of the tests) the jmods/java.base.jmod file is needed. However, to reduce the size of the Docker image the jmods directory is removed here:

oss-fuzz/infra/base-images/base-builder/install_java.sh

Line 24 in b011780

rm -rf $JAVA_HOME/jmods $JAVA_HOME/lib/src.zip

I have disabled ProGuard execution now as well and at least locally when manually invoking Maven this configuration seems to work.

[DavidKorczynski]

Wonderful, thanks for simplifying this!