chore: update gradle to 8.4

[derklaro]

Motivation

Gradle released a new version (8.4) recently and we should update.

Modification

Update Gradle to 8.4. There were some other changes that needed to be done as well for this:

1. I had to replace blossom with a custom task due to the missing gradle 8 support in v1 and v2 only using template files
2. The Project.buildDir method is deprecated and must be replaced with Project.layout.buildDirectory
3. Dynamically loading the junit launcher via gradle is now deprecated, therefore we need to add the junit launcher dependency ourself

Result

We can now fully use Gradle 8.4 without any deprecations (at least none that we can resolve).

Other context

Closes #1267