Update newtab stats to have locale-aware formatting

[bsclifton]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Fixes #5827

Auditors: @cezaraugusto, @jkup

Test Plan

1. Launch Brave and open a new tab
2. View the stats and ensure it looks correct
3. Go to Preferences and change your locale
4. Quit and go back to step 1 for as many locales as you wish to test

Screenshots

English (en-US)

French (fr-FR)

Japanese (ja-JP)

Spanish (es) - NOTE: looks like translations are missing

[bsclifton]

I'll create a follow up issue here for short-hand notation...
ex: 214k instead of 214,000

[bsclifton]

issue created to track abbreviation:
#5889

[jkup]

++ any benefit to using moment.js for this instead? I recall some talk of .toLocaleString being problematic?

[luixxiul]

In Japanese the comma is unnecessary. Neither whitespace nor comma should exist.

Still, as long as .toLocaleString() works like that, it should be like that...