Fix naming ambiguities in the APIs

[ascopes]

There are a few places in the API that have slight naming ambiguities.

An example:

• sourcePath - https://github.com/ascopes/java-compiler-testing/blob/main/java-compiler-testing/src/main/java/io/github/ascopes/jct/assertions/JctCompilationAssert.java#L317
• sourcePathPackage - https://github.com/ascopes/java-compiler-testing/blob/main/java-compiler-testing/src/main/java/io/github/ascopes/jct/workspaces/Workspace.java#L444

Let's decide on the right naming to use globally, and make new methods where needed to enforce this.

Let's then deprecate methods using the old naming, and remove them on the feature/v1.0.0 branch.

Make sure all documentation and tests are updated.