.pytool/Plugin/UncrustifyCheck: Output file diffs by default

.pytool/Plugin/UncrustifyCheck: Output file diffs by default

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3808

Changes the default for the "OutputFileDiffs" configuration option
to "True" so the formatting suggestions detected by Uncrustify
will be output in the test case log. The diff is printed in unified
diff format.

This was disabled by default during the initial enabling of
Uncrustify to reduce overall execution time of the plugin against
the codebase due to the large number of changes detected.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Rebecca Cran <quic_rcran@quicinc.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>