[lldb] [Process/NetBSD] Copy the recent improvements from FreeBSD

Copy the recent improvements from the FreeBSDRemote plugin, notably:

- moving event reporting setup into SetupTrace() helper

- adding more debug info into SIGTRAP handling

- handling user-generated (and unknown) SIGTRAP events

- adding missing error handling to the generic signal handler

- fixing attaching to processes

- switching watchpoint helpers to use llvm::Error

- minor style and formatting changes

This fixes a number of tests, mostly related to fixed attaching.

Differential Revision: https://reviews.llvm.org/D91167

lldb/test/API/python_api/hello_world/TestHelloWorld.py

@@ -74,7 +74,6 @@ class HelloWorldTestCase(TestBase):
 
     @add_test_categories(['pyapi'])
     @skipIfiOSSimulator
-    @expectedFailureNetBSD
     @skipIfReproducer # File synchronization is not supported during replay.
     def test_with_attach_to_process_with_id_api(self):
         """Create target, spawn a process, and attach to it with process id."""
@@ -108,7 +107,6 @@ class HelloWorldTestCase(TestBase):
     @add_test_categories(['pyapi'])
     @skipIfiOSSimulator
     @skipIfAsan # FIXME: Hangs indefinitely.
-    @expectedFailureNetBSD
     @skipIfReproducer # FIXME: Unexpected packet during (active) replay
     def test_with_attach_to_process_with_name_api(self):
         """Create target, spawn a process, and attach to it with process name."""