Document ERROR_NOT_FOUND exception for StoreContext.GetAppLicenseAsync

[Copilot]

Added missing exception documentation for the StoreContext.GetAppLicenseAsync method to address undocumented error cases.

Changes Made

Added an ## -exceptions section to document the ERROR_NOT_FOUND exception that can be thrown when the app license could not be found or retrieved. The documentation follows the established patterns used by other Store methods in the same namespace.

Specific addition:

• Documents System.Runtime.InteropServices.COMException with error code 0x80070490 (ERROR_NOT_FOUND)
• Provides clear explanation of when this exception occurs
• Maintains consistency with existing documentation format

Context

The issue reported that error cases were not documented for this method, specifically mentioning that it "can at a minimum throw an ERROR_NOT_FOUND exception under some circumstances." This change addresses that gap by providing explicit documentation for developers using this API.

The documentation now matches the format used by similar Store methods like RequestPurchaseAsync and RequestRateAndReviewAppAsync, ensuring consistency across the namespace.

Fixes #995.

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