Temporarily make ContribsPager properties public to unblock Flow

Temporarily make ContribsPager properties public to unblock Flow

This partially "reverts" Ic2367ca by explicitely marking the properties
Flow depends on as public. Before, these properties have not been
declared, but dynamically created. PHP marks dynamically created
properties as public by default.

Note that before Ic2367ca it was not even documented that these properties
exist. Flow was using undocumented code.

This revert is done to unblock the currently broken Beta cluster and
give us more time to find cleaner solutions. Some much more sustainable
solutions are discussed in T212771.

Bug: T212771
Change-Id: I2295a3fefe874a59458e6ea7edd2cfdd9e912096