Reclassify the Borealis launcher as a default app.

It can only get on a device by being preinstalled, so this seems
like a more appropriate category. More importantly, it should make
app count metrics slightly easier to interpret.

BUG=b:202065545
TEST=With Borealis enabled but not installed, view chrome://histograms to check that Apps.AppsCountPerInstallReason.Borealis.Preload is 1

Change-Id: Ie2768aa92921c8abe492b40236fb2931dac373a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3302293
Commit-Queue: Chloe Pelling <cpelling@google.com>
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Auto-Submit: Chloe Pelling <cpelling@google.com>
Reviewed-by: Nancy Wang <nancylingwang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#945543}