Prioritize the Binding Types property over local members when the BindingContext is set. Referring to a local member be explicit.

### Description

In XAML C# expression, prioritize the Binding Types property over local members when the BindingContext is set. When referring to a local member, be explicit, e.g., `this.Title`.

The current design returns an error, indicating ambiguity and suggesting adding a period. Doing so can affect the expression's readability.

### Public API Changes

Current flow to continue as it is. When the developer wants to refer to the local member, let them explicitly state it as `this.Member`. When there's no prefix, it refers to the member from the binding context.

### Intended Use-Case

Clarity of XAML C# Expression and a smooth migration.

Start by locating the XAML C# expression binding-resolution entry point and the tests covering BindingContext name lookup. Verify that unprefixed names prefer Binding Types when a BindingContext is set, while local members remain available through an explicit this.Member reference.

Written by the indexing model from the issue text.