Editor: Reset title scroll position on blur

[aduth]

Fixes #347

This pull request seeks to resolve an issue in Firefox where, after tabbing from the editor title field after having entered a very long title, the field would not reset to the start of the field.

Before:

After:

Testing instructions:

Verify that the title resets to the show the beginning of the field value when tabbing to the editor. This should behave correctly in Firefox and in your preferred browser.

1. Navigate to the Calypso post editor
2. Select a site, if prompted
3. Enter a long title, enough to scroll past the visible width of the editor
4. Tab from the field
5. Note that the beginning of the title field is visible

[nylen]

Confirming the bug and the fix. 👍

[blowery]

Is this something that should really be part of FormTextInput? Feels brittle to be monkeying with a DOM element from a custom element, as you don't really know what event.target is, or if it's the scrollable element.

[aduth]

Is this something that should really be part of FormTextInput? Feels brittle to be monkeying with a DOM element from a custom element.

That would depend whether we think browser quirks fall under the scope of behaviors to be implemented in the base form components. I'd personally lean towards keeping them as "pure" as possible such that their purpose is primarily aimed at keeping form styling consistent across the app. That said, an alternative view would be to consider them as normalized components, in which this would help keep behavior consistent across browsers.

[blowery]

Right. Either way, shouldn't hold the merge.