pmc: Move & generalize tools-specific build config to tools/metrics

Currently the build config for DWA is fully contained within
//components/metrics/dwa, even tools-specific code that directly
operates on files from //tools/metrics.  This patch moves this build
config to //tools/metrics and generalizes it so it can be used for
other Private Metrics types, e.g. DKM.

After this patch, each Private Metrics type will define two targets:
one for generating source code of builders from the XML file, and the
second one for building the code and providing a target that users can
depend on.

Bug: 433728659
Change-Id: Ica351603fbc82bbe08ecc35ab58e28125f8de576
Bypass-Check-License: Moving files around
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7002920
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Matt Dembski <dembski@google.com>
Commit-Queue: Matt Dembski <dembski@google.com>
Cr-Commit-Position: refs/heads/main@{#1525060}
NOKEYCHECK=True
GitOrigin-RevId: 15d6519cb164c6025c75a1c6f9a25fb217407b38