Add support for using extension methods in bindings

[acizmarik]

This PR allows using extension methods inside bindings. #903 should be merged first.

• Supported types to search for extension methods are defined within TypeRegistry
• Extension methods are searched only in case the basic method search fails
  • Regular methods are always preferred

Currently the only registered type to look for extension methods is System.Linq.Enumerable. This makes it easier to define lambdas when using LINQ.

• Initial lambdas support Add support for lambdas in command bindings #903: Enumerable.Where(Array, (int item) => item % 2 == 0)
• This PR introduces syntactic sugar: Array.Where((int item) => item % 2 == 0)

[exyi]

Very nice :)

[acizmarik]

To use custom extension methods you can:

• Implement own IExtensionsProvider or
• Extend the DefaultExtensionsProvider

This needs to be then registered using dependency injection. If user registers no implementation, DotVVM uses the DefaultExtensionsProvider that has already the Enumerable type registered

[tomasherceg]

Shall we cache this? I am afraid that this will browse the types and look for the methods every single time.

[acizmarik]

We probably should. The implementation now caches the result of the method call GetMethods(..) to avoid unnecessary reflection. Also the attribute ExtensionAttribute is now checked to ensure that we yield only extension methods