We used to use the mango SPI processor, but this had two major issues:
* ecj wouldn't run annotation processors, requiring a separate proc:only compile run with javac
* mangoSPI couldn't do incremental compilation, so this required a full rebuild just to generate SPI files, every time.

Addressed by updating to IPP40 which does support explicit annotation processors even for ecj, and
adding our own SPI generating annotation processor to the build which can deal with incrementals.

There are some limits; removing a `@Provides` annotation on an existing type will need a full clean to pick that up, for example.
These limits seem quite exotic, though.

These handlers had methods with humongous argument lists, and they needed to grow even more in order
to accommodate some new needs to properly implement checkerframework (where annos can be type-use
based, which means they were being put in the wrong place.

void foo(com.foo.@X Bar paramName) // correct
void foo(@X com.foo.Bar paramName) // wrong

For example, the CalledMethod annotation is a type-use annotation.

This commit covers both that refactor and fixing checkerframework generation.

Which 'flavour' is defined in lombok.config; applied to toString, equals, canEqual, and plural-form of `@Singular`.

A bit of a shadow feature because the checker framework folks need to do some work on their side.
this update makes lombok generate a few checker framework annotations (if configured to do so)
which let the checker framework add warnings and errors for example if you misuse builders, or ignore
the return values of withers, etc.