[csharp] Handle nested maps recursively

[devhl-labs]

Converts existing code into recursive code to better handle nested maps. First of a few PRs to fix issues pointed out by #21585 I don't think sample changes are necessary since its only making existing code recursive.

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[wing328]

suggestion: adding a docstring explaining what this function does

[devhl-labs]

Can we merge this and ill send a docstring in the next pr? Ive got three or four others queued up.

[wing328]

sure bro