Into `ServerEventListener` and `ClientEventListener`.

The new debugger implementation wants to listen to breakpoints being set so that traps can be dynamically enabled.

Bug: b/145351270
Change-Id: Iafe64426874da3aa109d4b59b34cb1e36bd06828
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48690
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Tested-by: Ben Clayton <bclayton@google.com>