[release/9.0] Fix stack overflow in the configuration source gen

[github-actions]

Backport of #106511 to release/9.0

/cc @ericstj @tarekgh

Customer Impact

• Customer reported

When using the configuration source generator on a type that has a cycle in it's generic parameter the source generator will crash with a stack overflow, eg:

public sealed class TreeElement : Dictionary<string, TreeElement>;

Regression

• No

Testing

Validated customer reported type, unit tests added.

Risk

Low, only impacts users of source generator and only paths where we inspect element types.

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[jeffhandley]

Approved for RC2. Reliability issue that we'd service for.

[ericstj]

/azp run

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[ericstj]

Build had the failure due to ILC problem. Rerunning to ensure we get a complete build.