Datagrid: Add a public API to get the current viewport #1795

Job	Run time
build	5m 50s
check_links	1m 30s
check_release	4m 54s
JS (ubuntu-latest, chrome-headless)	2m 51s
JS (ubuntu-latest, firefox-headless)	3m 5s
JS (windows-latest, chrome-headless)	5m 18s
JS (windows-latest, firefox-headless)	4m 48s
JS (windows-latest, webkit-headless)	4m 57s
JS (macos-latest, chrome-headless)	4m 54s
JS (macos-latest, firefox-headless)	7m 14s
JS (macos-latest, webkit-headless)	7m 23s
	52m 44s

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