Image paths in Resources/Raw for Android must be lowercase

See the document, where it states
>To comply with Android resource naming rules, all local image filenames must be lowercase, start and end with a letter character, and contain only alphanumeric characters or underscores. For more information, see [App resources overview](https://developer.android.com/guide/topics/resources/providing-resources) on developer.android.com.

I think this needs to be stressed much more clearly, and not just that filenames need be lowercase, but their paths too. There is also no documentation on how a user might still use the Assets folder in their Android project if their app still has one. This has been causing me no end of problems for a while now, so I think it needs more clearly documented, and possibly a bug raised to handle this lowercase only problem?

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#### Document Details

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* ID: cb4d16da-8c0f-5b7e-54ee-1fe36c549837
* Version Independent ID: cb4d16da-8c0f-5b7e-54ee-1fe36c549837
* Content: [Image - .NET MAUI](https://learn.microsoft.com/en-us/dotnet/maui/user-interface/controls/image)
* Content Source: [docs/user-interface/controls/image.md](https://github.com/dotnet/docs-maui/blob/main/docs/user-interface/controls/image.md)
* Product: **dotnet-mobile**
* Technology: **dotnet-maui**
* GitHub Login: @davidbritch
* Microsoft Alias: **dabritch**

Read docs/user-interface/controls/image.md and the linked Android App resources overview first. Update the image documentation to explain that Android resource paths as well as filenames must follow the lowercase naming rules, and document how to use an existing Assets folder. Done means both cases are clearly covered without leaving the behavior question ambiguous.

Written by the indexing model from the issue text.