[core] Disallow overriding a required property with an optional property

[witemple-msft]

Closes #3539

This change disallows overriding a required inherited property with an optional property.

This error does not take precedence over regular property assignability rules. In case the property both is optional when the overridden property is required and has a non-assignable type, both errors will be reported.

[azure-sdk]

All changed packages have been documented.

• ✅ @typespec/compiler

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@typespec/compiler - breaking ✏️

Disallows overriding a required inherited property with an optional property.,> ,> In previous versions of TypeSpec, it was possible to override a required property with an optional property. This is no longer allowed. This change may result in errors in your code if you were relying on this bug, but specifications that used this behavior are likely to have been exposed to errors resulting from incoherent type checking behavior.,> ,> The following example demonstrates the behavior that is no longer allowed:,> ,> tsp,> model Base {,> example: string;,> },> ,> model Child extends Base {,> example?: string;,> },> ,> ,> In this example, the Child model overrides the example property from the Base model with an optional property. This is no longer allowed.

[azure-sdk]

You can try these changes at https://cadlplayground.z22.web.core.windows.net/prs/3659/

Check the website changes at https://tspwebsitepr.z22.web.core.windows.net/prs/3659/

[witemple-msft]

Merging and will keep an eye on typespec-next to validate that there are no spec errors.