Add a check for enable_display_content_mode_management flag when

checking display.canHostTasks()

Since Display.canHostTasks is set only when
enable_display_content_mode_management is enabled, we should check the
flag before calling canHostTasks().

Bug: 452853149
Flag: com.android.server.display.feature.flags.enable_display_content_mode_management
Test: disable enable_display_content_mode_management and run
MultiDisplayPolicyTests#testSecondaryDisplayShowToast
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:570eab1d9ef9deaec9bfd7dac80908c3015be2b0
Merged-In: Ia9ebc36fe9386f82f43d125b60176d2cc2b8650d
Change-Id: Ia9ebc36fe9386f82f43d125b60176d2cc2b8650d