Edit to allow core and framework targets on the same build

[BryanAldrich]

When building for net framework and netcore, the csharp doesn't properly compile. e.g. references to DateOnly for the net472 build is what brought this to my attention.

I changed the mustache directives for net6 to be compiler directives instead. Due to new line requirements on the directives, this did require some symantical formatting changes. Other changes I removed entirely to keep the mustache logic a lot simpler. (e.g. the new () vs new Class() syntax).

@mandrean @shibayan @Blackclaws @lucamazzanti @iBicha

The notes below say for windows to run it in Git Bash, however, all of the line endings are messed up, I re-ran it in WSL so it is all proper linux endings.

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• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
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  ./mvnw clean package || exit
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  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
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[wing328]

cc @devhl-labs as well since the change impacts generichost

[wing328]

the CI builds still failed.

can you please take another look?

[devhl-labs]

I wont object to this but Id really like it if the mustache net6orlater and related were instead moved to the abstract. This is one of the issues with the C# generators, many settings ought to be in the abstract. Since they're not they get defined differently in each generator.

Also, if you haven't, please add a sample to ensure the error you saw does not get reintroduced.

[BryanAldrich]

@devhl-labs I updated the mixed targets sample that was in the 4.7 category. It now targets standard, 47 and 8. There are a few models now with the DateOnly support (which is net6+). Previously, this would have failed to compile on framework or standard.

[BryanAldrich]

@wing328 one of the automated builds failed, but i don't know how to resolve that.