Fix deadlock regarding screen-capture-disabled

- Introduced DevicePolicyCache, which stores a copy of device policies
that can be accessed with any lock held.

- Removed "wm screen-capture". According to code search, it's not being used,
and this command wasn't really working as intended, since DPM can always
override the manually set value.

Bug: 74277398
Test: atest /android/pi-dev/cts/hostsidetests/devicepolicy/src/com/android/cts/devicepolicy/MixedDeviceOwnerTest.java#testScreenCaptureDisabled,testScreenCaptureDisabled_assist ; \
Test: atest /android/pi-dev/cts/hostsidetests/devicepolicy/src/com/android/cts/devicepolicy/MixedProfileOwnerTest.java#testScreenCaptureDisabled,testScreenCaptureDisabled_assist ; \
Test: atest /android/pi-dev/cts/hostsidetests/devicepolicy/src/com/android/cts/devicepolicy/MixedManagedProfileOwnerTest.java#testScreenCaptureDisabled,testScreenCaptureDisabled_assist
Change-Id: I1968d1c32145a715d0343f25cb9d58939514b597