Avoid loss of ninja_deps events

Previously, writeDepFile was passed a copy of the main EventHandler to
which it then added an event. Adding an event requires appending
information to slices in the EventHandler structure. As the slices are
a copy the addition only affects the copy and are not present in the
EventHandler which is written out as part of the metrics.

This change fixes that by passing a pointer to an EventHandler into
writeDepFile. For consistency it also replaces a few other uses of
EventHandler with *EventHandler instead.

Bug: 257590265
Test: m nothing
      # Check generated text metrics to make sure they don't contain ninja_deps.
      # Apply this change.
      m nothing
      # Check generated text metrics to make sure they do contain  ninja_deps.
Change-Id: I0fa0f2b08844cb7c7b4e99b37602703deb43ad20