Add LoadTraceFromFile to SBDebugger and SBTrace

Add trace load functionality to SBDebugger via the `LoadTraceFromFile` method.
Update intelpt test case class to have `testTraceLoad` method so we can take advantage of
the testApiAndSB decorator to test both the CLI and SB without duplicating code.

Differential Revision: https://reviews.llvm.org/D128107