Use Context#startForegroundService in MTP provider

NotificationManager.startServiceInForeground() was moved to
Context#startForegroundService. MtpDocumentsProvider should use new one.

Bug: 36794559
Test: MtpDocumentsProviderTests
Change-Id: I84723ee8c3f0f8bfe4d5ea8ad035c01c42ce8bab
(cherry picked from commit 203be491ef479deea1f39f8b63f3e1916501a37a)
4 files changed