Text/TextArea Editors don't modify fields when `showIsPopup=true` and used in a GridModel from within a dialog

[minusleaf]

A client-app experienced this issue where the editor (in my case, the TextEditor and TextAreaEditor) wouldn't register the user's input, preventing fields from being edited.

Removing the showIsPopup flag does allow the editor to function as expected.

[jskupsik]

This can be fixed by unsetting the agOptions.popupParent from hoist default to null:

grid({agOptions: {popupParent: null}})

See xh/toolbox#775

[jskupsik]

Investigate why we default the value in Grid.ts:

            popupParent: document.querySelector('body'),

Perhaps we can just unset this and let ag-grid intelligently(?) pick a default popup parent location? Is there another case where not manually setting this produces a bug?

[jskupsik]

I've tracked down the original commit to: 66f7113

I don't think we want to break popups extending past/out of the grid, so we should NOT make this change in hoist.