[typescript-angular]: fix singleRequestParameter are always optional

[qirex]

Currently using the singleRequestParameter option to generates the angular services, the method signature will always set the single request parameter to optional even if all its properties are required.

This issue was reported and discussed in this PR: #18467
This PR fixes this behavior by using hasRequiredParams instead of hasRequiredVars to generate the method signature.

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[macjohnny]

thanks for the fix