Set preferred size for a pane

[johnwalley]

Purpose

As a developer I would like to set a preferred size for when the user double clicks a sash adjacent to a pane.

Proposal

Let's play with the idea of using defaultSizes purely for setting the sizes on initial mount. The main use case here is for applications to persist the layout.

We can then introduce a concept of preferred size purely for use when resetting the panes' layout.

A good starting point would be to look at the VS Code Grid component.

Acceptance criteria

• As a developer I can set a preferred size for a pane
• As a developer when I double clock a sash adjacent to a pane with a preferred size that pane should be set to that size (unless minimum or maximum size conflict)

[johnwalley]

A proof of concept. The sidebar has a preferred size of 300px.

[johnwalley]

We might need to introduce the internal concept of high/low priority views. What's currently happening is that the views are given the correct sizes. However, when we relayout, we distribute space from right to left. So if the last view has been shrunk, it will immediately be expanded to fill in the missing space!

[johnwalley]

It would be helpful to allow the preferred size to be dynamic, e.g.

[johnwalley]

Percentage based size would also be nice.

[johnwalley]

Make sure to consider the behaviour when adding a new frame. Should it take on its preferred size?

Also, what happens when we reset the whole split view? How should space be allotted amongst multiple panes with preferred sizes?