[dotnet] Return Task instead of wait it in generated CDP method invocations

[nvborisenko]

Description

Generated code for CDP is

public async Task Do()
{
  return await DoSomethingElse();
}

We can refactor it to

public Task Do()
{
  return DoSomethingElse();
}

Pros:

• More performant
• Compiler generates less IL code (dll size before: 6.5MB, after: 4.5MB)

Cons:

• Exceptions. raised by DoSomethingElse() method, don't indicate Do() method in stacktrace

Motivation and Context

Improve this amazing library.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the contributing document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.