Fix WTG3014/WTG3013 code-fix to emit explicit type argument when needed

[Copilot]

The Concat→Prepend/Append code-fix produces uncompilable code when the element type differs from the sequence element type. For example:

// Source: triggers WTG3014
var expected = new object[] { viewModel }.Concat(viewModel.Items);

// Before (broken - CS0411):
var expected = viewModel.Items.Prepend(viewModel);

// After (correct):
var expected = viewModel.Items.Prepend<object>(viewModel);

Changes

• LinqEnumerableCodeFixProvider now extracts the TypeSyntax directly from the array/object creation expression (e.g., object from new object[] { ... }) to determine the type argument — avoiding the expensive SemanticModel
• New GetCollectionElementType extracts the element type from ArrayCreationExpression or single-type-argument ObjectCreationExpression
• GetMethodName emits a GenericName node with Simplifier.Annotation when an explicit type is present, allowing Roslyn to remove it when redundant
• Added PrependTypeMismatch test data covering both Prepend and Append with mismatched types

[brian-reichle]

@copilot, using SemanticModel is expensive, so we should avoid it where possible. In this case, we should be able to take the TypeSyntax from the new array expression and use that as the type argument (after trimming trivia and adding Simplifier.Annotation).

[Copilot]

Done in ba72978. Replaced SemanticModel usage with syntactic extraction of the TypeSyntax from the array/object creation expression. The type argument is now annotated with Simplifier.Annotation so Roslyn removes it when it's redundant (e.g., new int[] { 5 }.Concat(a) still produces a.Prepend(5)).

[brian-reichle]

@copilot
ViewModel should be placed after Bob so that future changes are less likely to require location updates in Diagnostics.xml.

[Copilot]

Done in ba72978. Moved ViewModel after Bob in both Source.cs and Result.cs.