Use Intersection Observer API for in-viewport module

[xmlking]

Is your feature request related to a problem? Please describe.

use Intersection Observer API like

https://github.com/TradeMe/ng-defer-load

for in-viewport module

Describe the solution you'd like
A clear and concise description of what you want to happen.

Describe alternatives you've considered
use Intersection Observer API to check if an element is in viewport and falls back to scroll detection mechanism for unsupported browsers.

Additional context
Add any other context or screenshots about the feature request here.

[coryrylan]

Agree this would be a great improvement!

[xmlking]

here is my initial implementation
https://github.com/xmlking/ngx-starter-kit/tree/develop/libs/ngx-utils/src/lib/directives/in-viewport

demo
https://xmlking.github.io/ngx-starter-kit/dashboard/experiments/viewport