Merge parent-first jars into single jar

[geoand]

Relates to: #36099

[geoand]

@Sanne @franz1981 this is something to try and see if it brings in improvement in startup RSS.

[Sanne]

I've been trying to measure the impact of this - unfortunately while it seems the patch is doing exactly what I had in mind, the benefits are much smaller than I expected: heap size on a warmed up instance of the "getting-started" quickstart goes from about 4.1 MB to 3.9 MB.

To be clear, there are some benefits... I can clearly see them in a heap dump across several areas but just not as much as I expected.
Sorry, it seems like those zip header buffers are actually not that significant as I remembered they were - something seems to have changed in the JDK.

However I'd still like it if we could proceed in this direction: having that single jar would be a step to then experiment with those other ideas.

BTW we technically have two jars now as output: there's the "quarkus-run.jar" in the root and the "lib/boot/quarkus-boot-lib.jar" - to make it possible to experiment with alternative formats perhaps these should be fused as well?

[geoand]

BTW we technically have two jars now as output: there's the "quarkus-run.jar" in the root and the "lib/boot/quarkus-boot-lib.jar" - to make it possible to experiment with alternative formats perhaps these should be fused as well?

Sure yeah, I can try that

[geoand]

@Sanne I pushed a commit that removes the boot jar completely and just moves everything into quarkus-run.jar