[csharp] fix "Simplify 'default' expression (IDE0034)" messages

[ffabss]

This PR adjusts the csharp code generation to directly use default instead of default({{&dataType}}). Thereby it gets rid of a few hundred IDE0034 messages and also reduces the overall size of the code a bit.

There are a lot of changed files but essentially the changes are only in the mustache files for c#. There all occurrences of the regex default\([^)]*\) are replaced by default.

I checked the (changed) samples to verify that they still build and that the messages are gone.

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[wing328]

thanks for the PR

also cc @devhl-labs