Remove `GetValueGenerationStrategy` overload with `ITypeMappingSource` parameter

[dmitry-lipetsk]

EF 6.0.

Current declaration of ITypeMappingSource::FindMapping(property) requires reference to IProperty.

efcore/src/EFCore.Relational/Storage/IRelationalTypeMappingSource.cs

Line 40 in b38c269

new RelationalTypeMapping? FindMapping(IProperty property);

As result, in some code need cast resference of IReadOnlyProperty to IProperty.

For example:

efcore/src/EFCore.SqlServer/Extensions/SqlServerPropertyExtensions.cs

Line 572 in b38c269

?? typeMappingSource?.FindMapping((IProperty)property))?.Converter;

This cast looks as a problem in interface design.

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If I understand everything correctly, IReadOnlyProperty interface is enough for ITypeMappingSource::FIndMapping(property).

Or no?

[AndriySvyryd]

Normally, ITypeMappingSource.FindMapping(property) should only be called on a finalized model as it's a relatively expensive operation and we can't memoize the result if the model is still mutable.

In the case above we had to call it as it was needed for a convention, but I hope #9329 will allow to rewrite that convention and remove the FindMapping call.