Add smoothScroll to scrollLines

[tisilent]

Fix #4121

[tisilent]

@Tyriar hi. help review.

[Tyriar]

Thanks @tisilent, I made some changes to fix the tests and pass the scroll to top/bottom/line/pages calls through scrollLines

[tisilent]

Oho @Tyriar , learning to write testsI'm learning to write tests .
I'm thinking about some of the logic of Terminal scrollLine moving to Viewport.
Terminal -> Viewport -> BufferService

[Tyriar]

Test coverage is good enough currently, there are unit tests which run in node and use a Mock Viewport and then API tests that actually use the scroll apis in a browser context

[tisilent]

no.no. I learned how to write tests，Thanks @Tyriar

[tisilent]

I’am very sorry I had a wrong to sent the message. @Tyriar
learning to write tests
I'm learning to write tests .
😓