Grid/DataCommunicator should align data queries to a page size

In order to make it possible to create an efficient data provider based on a paging data source (many many data sources are page based, e.g. Spring Data), grid should define and provide a page size it will be used when querying the data provider. Queries to the data provider should then always be for a full page of the same page size to reduce backend traffic.

Potentially the developer wants to affect the page size, but the most important is to be able to GET the page size used and being able to rely on queries being aligned to page boundaries.

If the request data in #8982 still holds true, i.e.:
offset 0 limit40
offset 40 limit50
offset 50 limit40
offset 80 limit19
offset 95 limit5

then it would be quite inefficient to use a paging data provider unless you happen to guess a suitable page size. If you guess based on the intial query, you would do requests for:
0-40
40-80
40-80-120
80-120
80-120

This is quite far from the optimal of requesting each of the three pages once

Start by reviewing the Grid/DataCommunicator query behavior and the request described in #8982. Determine how page size and page-boundary alignment should work, including whether developers can configure it; done means data-provider queries consistently request aligned full pages and expose the page size.