Notify client on all dmypy crashes (#7593)

This is done by setting the raise_exceptions option, which will cause
the exception to continue to be propagated.
Closes #4804.

Tested by introducing a crash in the parser and verifying the message
came through.

mypy/dmypy_server.py

diff --git a/mypy/dmypy_server.py b/mypy/dmypy_server.py
index 3a3f43e..0c1c844 100644
--- a/mypy/dmypy_server.py
+++ b/mypy/dmypy_server.py
@@ -175,6 +175,7 @@
 
         self.fscache = FileSystemCache()
 
+        options.raise_exceptions = True
         options.incremental = True
         options.fine_grained_incremental = True
         options.show_traceback = True