Style cleanup Thread and its tests

- Avoid implicit conversion of pointers to boolean
https://abseil.io/tips/141
- Prefer make_unique instead of raw new
https://abseil.io/tips/126
- Wrap single-line conditional statements with {}
lack of braces is allowed, but discouraged by style guide: go/cstyle#Formatting_Looping_Branching
- rename member variables to follow naming convention
https://google.github.io/styleguide/cppguide.html#Variable_Names
- use c++20 std::erase instead of manual search in erase in vector
- In tests prefer to create threads without SocketServer when tested logic doesn't rely on one
https://issues.webrtc.org/issues/42223331
- unwrap auto into actual type used.
- apply swap_gtest_args script to put expected values as 1st argument


Bug: None
Change-Id: Ieaa3a0ed0a8b8319e7d77bc153306030a546db59
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/474501
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Auto-Submit: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47779}