Improve APIs for IEdmModel look ups and traversal

[habbes]

The model provides a lot of APIs for traversing and querying elements in the model. However, a lot of this APIs are insufficient or limited, leading to expensive lookup operations.

Here are example of things that are difficult to do and lead to inefficient traversals

• Finding all properties in a model, or finding properties that meet a certain criteria. Currently, to find properties, you need to go through the collection of entity and complex types, e.g. model.SchemaElements.OfType<IEdmStructuredType()>().SelectMany(t => t.DeclaredProperties)
• Finding a type or property using a span (to avoid substring allocations) related: 2801
• Finding a type or property by name, using case-insensitive or custom comparer. In the past, we have resorted to reading all elements that need to be looked up and caching them in a separate dictionary with case-insensitive comparer, see: Create cache to speed up case-insensitive look up of schema elements #2610
• etc.

Assemblies affected

Microsoft.OData.Edm 8.x

[corranrogue9]

Let's create an ADO item to track this and split the work between breaking and non-breaking. Let's call non-breaking p2 items and breaking p3 for the next major version rev, with the planning and design for breaking as p2.

[corranrogue9]

@habbes to follow up with David and create the ADO item