Upgrade Gdx Setup to generate projects using Gradle 8.4

[obigu]

Not to merge before #7246.

The only required change has been to remove the following line from the html module build.gradle as the property doesn't appear to exist on the latest GWT plugin version.

checkGwt.war = file("war")

Would be great if somebody could confirm how important this line is.

EDITED
Another change has been made to disable R8 full mode which is set to true by default on AGP 8 (was false https://developer.android.com/build/releases/past-releases/agp-8-0-0-release-notes). Main issue with full mode is it removes implicit empty constructors which are quite commonly used by libGDX ReflectionPool (espcially Scene 2d classes). Should be possible to enable Full mode by adding some Proguard rules to keep the necessary empty constructors but it's not easy to make sure some will be missing and unexpected runtime errors occur. For the moment I think it's best to keep using old well tested Proguard rules by default.

[tommyettinger]

It isn't important; it was needed to do some verification task in an older Gradle/GWT-plugin version, but isn't needed now. Liftoff hasn't included that line for a while; it looks like I removed it 17 months ago.

[SimonIT]

By the way, it seems that the gwt-gradle-plugin has changed its package to org.docstr: new plugin page (commit). So there's already version 1.1.29

[tommyettinger]

I definitely agree about R8 full mode; it will be (or was just) set to disabled by default in new Liftoff projects because of how much trouble it causes during minimization. I still think we should update to Gradle 8.4, considering how infrequently gdx-setup updates.

[obigu]

I still think we should update to Gradle 8.4, considering how infrequently gdx-setup updates.

Before upgrading I run tests on all platforms which takes time. On the other hand 8.4 has just been released and it's possible 8.4.1 (or even 8.5) is released by the time this is merged.

If no new Gradle releases occur in the next few days I will test and upgrade but the change should be trivial for client apps so I'm not very concerned about it.