Refactor SQLite compilation tasks

[simolus3]

On all native platforms we currently support, we compile and link a copy of SQLite statically (through the :static-sqlite-driver project).

The way the compilation is currently set up is a suboptimal, as it doesn't allow Gradle to cache outputs effectively:

1. We're using dependsOn to specify task dependencies, which is not recommended. We should specify file dependencies instead, as that allows Gradle to understand the dependencies better and allows for fine-grained build invalidation.
2. A lot of the compilation tasks we written using Exec, which does not support caching. To make the build easier to understand while also improving cache invalidation, I've extracted the tasks into independent files.

Finally, I've enabled the build cache, which should allow us to cache outputs (including the compiled sqlite libraries) across CI runs, avoiding a recompilation on every run.