Enable kSystemNudgeV2 flag (go/anchored-nudges)

Enable the use of the new SystemNudgeView as it is already being used in
production, mainly by the VideoConference feature. [1]

Example nudges that use this new view are listed in the NudgeCatalogName
enum that exists in notifier_catalogs.h [2].

This view is stable ready and planned to be used by other feature teams, such as by the 10-in-7 in-product-help framework [3], focus mode [4], game dashboard, etc. so enabling the flag to allow its use is necessary.

[1] https://docs.google.com/presentation/d/1ZjTIsT3W72x99Tn5YlrqmDKlDGhzeaudgvtKUE0ArZk/edit?resourcekey=0-V_LGCie4s5JhRA2SQHWEfA#slide=id.g257d32fee0c_0_9

[2] https://source.chromium.org/chromium/chromium/src/+/main:ash/constants/notifier_catalogs.h;l=213-221;drc=9939fcf932f9b71bd271667e4dbca68a937ae74b

[3] https://docs.google.com/presentation/d/1_viSSXff0TQZL3oxji-5Snu6RcNzVHnttXlGWVZ4bi4/edit?resourcekey=0-pCy3Qc7PEyQclOTfBrxWhw#slide=id.g2521111800e_0_276

[4] https://docs.google.com/presentation/d/1PsG54G0nT6TzgqppEPmkSlYGs9ccBTMrvJrPPR69gT4/edit#slide=id.g27e29c8ce52_0_55

Bug: b:305257026
Change-Id: I3d06a5537fede3c23a2124a181ad90c57388ddf7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4950482
Reviewed-by: Alex Newcomer <newcomer@chromium.org>
Commit-Queue: Kevin Radtke <kradtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1211642}