[aot repositories] smoothen support for repository aot sources/metadata

[martinlippert]

The idea is to make it a lot easier to produce the AOT generated sources/metadata for Spring Data repositories (if applicable) from inside of the IDE.

This incudes:

• produce the AOT bits via a command or (even better) incrementally while working with the project inside of the IDE
• integrate the generated sources as source folders to allow setting breakpoints, etc.

[BoykoAlex]

The command piece is being implemented in #1713