Improve operator<< for structs and arrays

[Kronos3]

Before this PR, operator<< was implemented for structs and arrays by calling out to toString().

There are two problems with this approach:

1. If you define operator<< for an abstract type inside a struct, it will not be called.
2. If you try to implement toString() and run out of space in the Fw::StringBase buffer you are writing to, the string gets truncated

• This is not at all optimal for unit tests where operator<< is enabled.

I needed this change when working on nasa/fprime#4890 (not a tandem just useful for debugging).

[bocchino]

Some notes:

• We will need to review and merge Fix code gen for empty structs #966 before merging this PR. Some conflict resolution will be required, but it shouldn't be too bad, as the Scala code changes are localized.
• We should defer this merge until after releasing v3.2.0 (or make a release branch and merge this into main).

[bocchino]

Also I think this is a tandem PR because it changes the behavior of <<, so it will require tandem changes to FppTest.