context: replace transport socket context with generic context

[wbpcode]

Commit Message: context: replace transport socket context with generic context

Additional Description:

Now the transport factory context share same interface with generic context. We removed the transport socket factory context and use generic factory context as althernative.

This PR:

1. removed TransportSocketFactoryContext and implementation.
2. replaced all TransportSocketFactoryContext with GenericFactoryContext.
3. Unified scope() to statsScope(). (The original TransportSocketFactoryContext use the statsScope(), but GenericFactoryContext use the scope(), this PR change all to statsScope())

Risk Level: low. mainly simple symbol replacement.
Testing: n/a.
Docs Changes: n/a.
Release Notes: n/a.
Platform Specific Features: n/a.

[repokitteh-read-only]

CC @envoyproxy/coverage-shephards: FYI only for changes made to (test/per_file_coverage.sh).
envoyproxy/coverage-shephards assignee is @RyanTheOptimist

🐱

Caused by: #39201 was opened by wbpcode.

see: more, trace.