[Shared] Add non-task helper to execute tool

[LexManos]

Would be nice to be able to execute a tool without using the ToolExec task.
Namely, without giving users all the extra ways to configure I wanted to execute a tool twice in one task. For Srg2Source, need to execute it to extract and apply the rangemap.

[Jonathing]

I've been experimenting several ways to make this work. Unfortunately, it's not easy. The best thing I can think of is something similar to our new MavenizerInstance system we have in FG7 for configuration time. And non-task interfaces need to be @Nested among other things to make configuration cache happy.

See this branch for my unfinished work regarding this. That being said, I'll probably end up starting from scratch on this front.

[LexManos]

Not a major rush, just ran into it again moving Srg2Source to renamer-gradle so made an issue to track it as a feature request for the future.