Replace use of SimpleStringBuilder with StringBuilder

Deprecate the SimpleStringBuilder class and migrate all existing usages
to StringBuilder in webrtc. This makes string construction across the
codebase more consistent and eliminates the need for manually manage
fixed-size buffers, which reduces boilerplate and mitigates the risk of
buffer overflows.

Key modifications:
* Mark the SimpleStringBuilder implementation as deprecated.
* Update StringBuilder to support appending `char` via operator<<.
* Refactor multiple implementation details — including API, audio,
  video, and test utilities—to use StringBuilder.
* Update function signatures to accept StringBuilder pointers or
  references where applicable.
* Simplified string generation in various ToString() methods by
  removing local character array buffers and use .Release() instead
  of .str() where appropriate.

Bug: webrtc:500767594
Change-Id: I738a78a176c17242e51190a4ac073080787d3d24
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/462202
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47374}