locksettings: move credentialTypeToString to LockPatternUtils

In preparation for using credentialTypeToString() from more places, move
it to LockPatternUtils.  Also change the strings returned to all
upper-case, as this looks better in the contexts where it will be used.

Bug: 268526331
Change-Id: Ic9ef28321bca793161182730d11a818378f8ab19
Merged-In: Ic9ef28321bca793161182730d11a818378f8ab19
(cherry picked from commit cacb0f37)