Stop auto scrolling to bottom on output

[parisk]

This PR is a continuation of #326 by @jupe. I kept all original commits, to maintain the appropriate credits 😊 .

This PR introduces this new behavior:

• When the user has scrolled up the terminal and output is being printed (by the back-end), the terminal now is not scrolling down to bottom, as it used to
• The terminal scrolls down to bottom when the user presses a key

Closes #216.

/cc @Tyriar to take a look since you opened the initial issue and commented also in the original PR.

[Tyriar]

Should this.userScrolling be set here?

Also I think having this at the start of keyDown means that the DOM could be updated twice in a row, once before the key is evaluated and once after.

[parisk]

Should this.userScrolling be set here?

I am not sure if it should. Strictly speaking, the user is not scrolling here. We are scrolling to bottom for them, in order to be able to see their input.

Also I think having this at the start of keyDown means that the DOM could be updated twice in a row, once before the key is evaluated and once after.

That's true. I put it there because I thought that we should scroll down no matter how the key will be handled (sounds like a universal terminal behavior).

I think it's not bad that the DOM might get updated twice, since this will happen only if the terminal needs to scroll down, meaning that in the next typing there will be no scrolling of the viewport, thus no second (or first 😄 ) DOM update.

[Tyriar]

Would it be easy to write some unit tests for this? For example:

• Key down always scrolls to bottom of buffer
• Write scrolls down to bottom of buffer when it's already at the bottom
• Write does not scroll down to bottom of buffer when not at the bottom

[parisk]

🆗 I moved on with the following:

1. Used scrollToBottom instead of manipulating ydisp and ybase myself and emitting scroll
2. Implemented test to make sure that terminal scrolls to bottom, when scrolled up and key is pressed
3. Cleaned up and squashed commits in order to avoid touching the dist directory at all and keeping the initial commit of @jupe.

@Tyriar I don't think I could easily implement tests for write as it interacts with the DOM heavily.

Let me know if this is good to go.

[Tyriar]

Clever trick 😄

[parisk]

Thanks!

[parisk]

@onttoni just letting you know that we mentioned you for your commit in this PR in the 2.1 announcement. Thank you!