DO NOT MERGE Fix mTrustManager NPE

When isDeviceLocked function is called in KeyguardManager, mTrustManager
can be null. To prevent NPE during this call, moved the mTrustManager
access to a synchronized getter.

Test: run cts -c android.print.cts.PageRangeAdjustmentTest -m testWantedPagesAlreadyWrittenForPreview
Test: run cts -c android.accessibilityservice.cts.AccessibilityEndToEndTest -m testTypeViewTextChangedAccessibilityEvent
Test: run cts -c com.android.cts.appsecurity.DocumentsTest -m testCreateExisting
Test: run cts -c com.android.cts.devicepolicy.ManagedProfileTest -m testCrossProfileCopyPaste
Test: run cts -c android.text.method.cts.PasswordTransformationMethodTest

Bug: 69471788
Change-Id: I4b4a0bb3b127424fecdad85ba559ce861af165e4