Fix the text alignment of the "Passphrase" hint string in RTL languages

Before this CL, the hint string of the passphrase EditText in
sync_enter_passphrase view was left aligned regardless the direction of
Chrome language. Now, it gets aligned depending on the direction of the
language.

...see screenshots of the fix,
LTR: http://screen/6ziHhgvWdrvneED
RTL: http://screen/6Xce3B2vgQstiPJ

Fixed: 428614149
Change-Id: I4f183cf43f245163a2993d7fef18eb68fe70d922
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6983509
Reviewed-by: Ankush Singh <ankushkush@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Mahmoud Rashad <mmrashad@google.com>
Cr-Commit-Position: refs/heads/main@{#1521139}