A `SetFunctionBreakpointsRequest` contains the full list of breakpoints. Clear the list in the context before adding the new list.

Also add a `getFunctionBreakpoints()` accessor so you can enumerate the list of function breakpoints.

Bug: b/145351270
Change-Id: Ia7fad403eace7a95a15671e2ce90b8e083da3ce7
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48694Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>