[DO NOT MERGE] Pre-allocate height for contextual cards.

To prevent the UI jank causing by the async card loads, we pre-allocate
some space for the card to fill in. After this change, only one card can
be shown at a time.

More details:
- When the card number configuration is set to 0, don't trigger the card
loader.
- The height adjusting logic is as follows.
When Settings is opened, pre-allocate a space first.
After the RV finish laying out, reset the RV to wrap_content. So if the
card has to be expanded(eg. wifi large mode or dismissal view), then it
will adjust the height accordingly. While if a card previously shown
becomes unavailable(dismissed or conditions not meet), we also reset the
RV so the space can be gone.

Bug: 163288869
Test: robotest
Change-Id: I0dcb2dae8f0533e562ad06f664b7ae7a9afecd21

res/values/dimens.xml

@@ -348,6 +348,7 @@
     <dimen name="contextual_half_card_padding_top">12dp</dimen>
     <dimen name="contextual_half_card_padding_bottom">16dp</dimen>
     <dimen name="contextual_half_card_title_margin_top">12dp</dimen>
+    <dimen name="contextual_card_preallocated_height">0dp</dimen>
 
     <!-- Homepage dismissal cards size and padding -->
     <dimen name="contextual_card_dismissal_margin_top">12dp</dimen>