Add r.session.data.pageSize

[renkun-ken]

What problem did you solve?

Closes #1067

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Adjust r.session.data.pageSize to 100, 500 and 0 and View(data.frame(id = 1:1000)) and see if the setting applies properly.

[eitsupi]

Just a question: what good does it do to reduce the page size? (display performance?)
My understanding is that all data is read regardless of page size, so the initial value for page size seems like it should be larger.

[renkun-ken]

I think it only affects the rendering performance, as larger page size means more objects in the WebView. Also, if the page size is too large, the scrolling will be harder to locate certain rows.

Here, the default value 100 comes from ag-grid. Maybe we could use 500.