trace2: add performance format target

[ldennington]

This series adds the performance format target for TRACE2 tracing.

The first two patches are small fixes for bugs I noticed as I was testing the
performance format target. The first moves the FormatTargetTypes enum
from the specific Trace2StreamWriter class to the shared Trace2Writer
class. The second ensures the normal format event names are written in snake
case (rather than lowercase).

The third patch adds the ability to get the "depth" of the process. Because Sids
and depth are process-related concepts, it removes the SidManager class and
moved depth/sid-related properties and methods into the ProcessManager class.

The fourth patch adds the performance format target. It includes a few notable
components:

1. A new GetMessage method to ensure message strings written to normal and
   performance targets are not duplicated.
2. A new PerformanceFormatComponent class to track sizing of optional
   properties of performance format messages.
3. A BuildSpan method that Trace2Message children use to create
   correctly-sized "spans" for optional properties of performance format
   messages. A span is a piece of the message beginning with a pipe (|) and
   ending just before the next pipe or the end of the message.
4. A BuildTimeSpan method that adjusts spans for long/short times. In
   future, when we have events that include performance format string span
   components, we will need to add an additional method to handle them.

[mjcheetham]

Had a few suggestions on improving perf/caching values, simplifying the virtual methods on Trace2Message, and wondered if we could avoid reflection at all.

[ldennington]

@mjcheetham @jeffhostetler - I believe all feedback has been addressed with my latest push, but please do let me know if I missed anything.

Edit: I did push changes after originally posting this, but that was only to clean up some merge conflicts with the PR that @mjcheetham merged to main earlier today and to fix a Windows/.NET Framework breakage.

[mjcheetham]

Looks great! Good stuff :)