Correct the fileName parmeter description for WASDK ResourceLoader(String fileName) constructor

[lauren-ciha]

This PR updates the description for the fileName parameter required for Windows App SDK's ResourceLoader.String() constructor. The fileName parameter takes in the path to a .pri file, not a resourceMap. The description added matches the description for the same parameter in ResourceLoader(String, String), which was introduced at the same time as the one-parameter constructor.

See Windows App SDK Issue #2406 - ResourceLoader can not load the specified resource.

[lauren-ciha]

Looping in @huichen123

[GrantMeStrength]

The ResourceLoader(String) constructor has two distinct use cases that this PR collapses into one. The original documentation ("resource identifier treated as a URI fragment") described the common case: passing a simple name like "Errors" to access a ResourceMap by name, which looks up resources relative to errors.resw or errors.resjson. The new text only describes loading by PRI file path, which is the less common case. A developer who writes new ResourceLoader("Errors") will be confused if the docs only mention PRI file paths. Please retain the resource-map-identifier explanation as the primary case, and add the PRI file path as a secondary note if applicable.

[GrantMeStrength]

@copilot /review

[GrantMeStrength]

Review: Needs Verification

This PR changes the ResourceLoader constructor description from loading a "resource map" to loading a "PRI file."

ResourceLoader doesn't directly load PRI files by path — it accesses named resource maps within the app's resource infrastructure. The parameter is a resource map identifier (e.g., "Errors" maps to resources in errors.resw), not a file system path to a .pri file.

Please verify this semantic change is accurate before merging.