[dotnet] [bidi] Align CapabilityResponse type name with spec - #18099

https://w3c.github.io/webdriver-bidi/#cddl-type-sessionnew

Spec defined anonymous type to be CapabilityResponse.

💥 What does this PR do?

This pull request updates type definitions related to session capabilities in the BiDi WebDriver implementation. The main change is the renaming of the Capabilities record to CapabilityResponse, which also affects its usage in related types.

Type definition updates:

• Renamed the Capabilities record to CapabilityResponse in dotnet/src/webdriver/BiDi/Session/New.cs to clarify its purpose and usage.
• Updated the NewResult record to use CapabilityResponse instead of the old Capabilities type for its Capabilities property.

🤖 AI assistance

• No substantial AI assistance used
• AI assisted (complete below)
  • Tool(s):
  • What was generated:
  • I reviewed all AI output and can explain the change

🔄 Types of changes

• Cleanup (formatting, renaming)