Added code generation for OnXyz and SendXyz methods (1/2)

[david-driscoll]

This is part one that only includes a few file changes to make the objective a little clearer. the next is just a bunch of deleted code (yay deleted code! 🥳 )

[david-driscoll]

TLDR: I'm sick of trying to keep all the methods in sync, but want to offer both an interface and delegate based interface for every handler. This solves that since handlers follow a fairly common pattern.

[codecov]

Codecov Report

Merging #256 into master will increase coverage by 0.01%.
The diff coverage is 61.85%.

@@            Coverage Diff             @@
##           master     #256      +/-   ##
==========================================
+ Coverage   62.06%   62.07%   +0.01%     
==========================================
  Files         383      387       +4     
  Lines       11489    12605    +1116     
  Branches     1361     1456      +95     
==========================================
+ Hits         7131     7825     +694     
- Misses       3788     4178     +390     
- Partials      570      602      +32     

Impacted Files	Coverage Δ
...nRpc/Generation/GenerateHandlerMethodsAttribute.cs	0.00% <0.00%> (ø)
...nRpc/Generation/GenerateRequestMethodsAttribute.cs	0.00% <0.00%> (ø)
src/Protocol/Document/ITypeDefinitionHandler.cs	0.00% <ø> (-52.55%)	⬇️
src/Protocol/General/IShutdownHandler.cs	0.00% <ø> (-70.84%)	⬇️
src/JsonRpc.Generators/Helpers.cs	57.10% <57.10%> (ø)
...nRpc.Generators/GenerateHandlerMethodsGenerator.cs	65.87% <65.87%> (ø)
...nRpc.Generators/GenerateRequestMethodsGenerator.cs	71.98% <71.98%> (ø)
src/JsonRpc.Generators/GeneratorDiagnostics.cs	100.00% <100.00%> (ø)
... and 6 more

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[NTaylorMullen]

Really cool idea! First seeing source generators in action. How was the dev experience with em?

[david-driscoll]

@NTaylorMullen I was actually pretty pleased with it. I have not played with the latest source generators but I assume they would be fairly similar. Sometimes I'd break things literally in half, break the generator, and using generated methods and things fall apart fast... however that's what unit tests are for.

[TylerLeonhardt]

I can't really judge the generator code cause I don't have the domain expertise, but I'm so excited to have all the On/Send messages available.