[MSBuild] Smart way to generate code only if changed

[xperiandri]

I suppose we need to create a cache file with the MSBuild task version and a map of the file name and its hash.
In the next generation, the task will read the cache and compare the MSBuild task version. If it is different then remove all and generate.
Then compare files lists, if they are equivalent then hash each file and compare hashes.
If lists are different or any GraphQL file is different, then remove all and generate.

@dim-37 @Zaid-Ajaj what do you think?

[njlr]

I would definitely keep an eye on Bazel, which excels at this kind of thing. The F# rules are still pretty early though: https://github.com/bazelbuild/rules_dotnet