Increase lint JVM heap size to 4GB

This aligns with the heap sizes used for D8/R8/javac. If needed, we can
increase further to 8GB to align with ErrorProne and avoid transient OOM
issues for certain targets.

Bug: 387971153
Test: m + presubmit
Flag: EXEMPT bugfix
Change-Id: I00f2d8f26121f7b48df80c5d14a222d550d9228c