Show placeholder for disabled widgets

When the setting for "Allow any widget in hub mode" is off, show
placeholders for widgets that are previously added but don't have the
allowed widget category specified.
Added the DisabledWidget content model to render widget in a disabled state.

Bug: b/324455650
Test: turn on the setting, add some non-keyguard widgets then turn off the setting
Test: atest CommunalInteractorTest
Flag: ACONFIG com.android.systemui.communal_hub STAGING
Change-Id: Ibad25f142b2add2c08451cffcfc4fad84afa0f81