[SwiftBindings] Added basic C# file support and file writing code

[stephen-hawley]

This adds the basic elements needed to support a simple (empty) C# file with the modern namespace declaration.
This adds a simple CodeWriter for writing elements out.
This adds the elements for C#:

• CSNamespace - a namespace declaration
• CSUsing - a using statement
• CSUsingPackages - a collection of using statements
• CSComment - a single line comment
• CSCommentBlock - a collection of single line comments
• CSTopLevelDeclarations - a collection of top-level declaration objects

Note that several of these types have the fluent method "And" which is useful for chaining things together.
for example:

var comments = new CSCommentBlock().And("Copyright (c) Microsoft Corporation.").And("Licensed under the MIT License.");

[kotlarmilos]

Remove src/Swift.Runtime/src/Metadata/TypeMetadata.cs, I guess it was added by mistake.

[kotlarmilos]

Is this needed?

[kotlarmilos]

Isn't this part of the emitter's environment? This should be known by parsing the ABI.

[kotlarmilos]

Isn't this part of the emitter's environment? This should be known by parsing the ABI.

[kotlarmilos]

Note that several of these types have the fluent method "And" which is useful for chaining things together.
for example:

var comments = new CSCommentBlock().And("Copyright (c) Microsoft Corporation.").And("Licensed under the MIT License.");

We need this in the string-based emitter as well. I suggest extracting it from the Dynamo.

[jkotas]

var comments = new CSCommentBlock().And("Copyright (c) Microsoft Corporation.").And("Licensed under the MIT License.");

This is a fine example. We should not be emitting license headers like this into the generated bindings. The binding generator is a compiler. The default licensing for compiler outputs is that compiler outputs are redistributable without additional restrictions. The only restrictions are based on the license of the compiler inputs used to produce the output.