Use SetterInput for more setters

[griff]

This changes more of the setters both manually implemented and generated to accept a SetterInput.

This makes it useful to implement SetterInput on your own types to support using them with setters.

This is especially useful when you have plain rust structs the represent the capnp-struct and you just want convert one to the other and is my main use case.

I don't know if this is a breaking change like how originally implementing SetterInput was.

[codecov]

Codecov Report

❌ Patch coverage is 65.38462% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.75%. Comparing base (ab342b3) to head (083b39c).
⚠️ Report is 192 commits behind head on master.

Files with missing lines	Patch %	Lines
capnpc/src/codegen.rs	0.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #578      +/-   ##
==========================================
- Coverage   51.64%   50.75%   -0.90%     
==========================================
  Files          69       70       +1     
  Lines       33735    32315    -1420     
==========================================
- Hits        17422    16400    -1022     
+ Misses      16313    15915     -398     

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[dwrensha]

Thanks. I can see how this could be useful, but I'm a bit worried about adding more complexity to the user-facing interfaces in the generated code.

[griff]

What do you mean by "adding more complexity"? You can already implement SetterInput for your own structs and use that where the setter supports it so Data and Text. this only makes SetterInput useful in other places.

But I can see making it more useful means more people using what might be considered an internal trait. If it is truly internal have you considered sealing it so others can't implement it then?

Also how would you then see making it easier to convert between generated types and plain rust structs?