Fetch KeyguardDisabledFeatures from DPE in getTrustAgentConfiguration()

- This is required for when
  SetKeyguardDisabledFeaturesCoexistence feature flag is enabled.

Test: atest with flag on/off with the following tests: android.devicepolicy.cts.KeyguardDisabledFeaturesTest android.devicepolicy.cts.KeyguardTest android.devicepolicy.cts.TrustAgentInfoTest com.android.cts.deviceandprofileowner.KeyguardDisabledFeaturesTest com.android.cts.devicepolicy.ManagedProfileTest
Flag: android.app.admin.flags.set_keyguard_disabled_features_coexistence
Bug: 385315558
Change-Id: Ie8c2e73afa16f7c488b6db86bf723a898b3ec793