Summary:
Diff makes side panels slide horizontally when opening/closing them.
Caveats:
. Right panel: even though the panel do transition nicely, the content however disappears suddently. We could prevent disposal of the dom by removing the two below lines. But it's hard to tell what possible side effect we could get from it as I don't know why these line were added in the first place. I could investigate further, but maybe it's already good enough as it is.
```
private _buildContentDom() {
return dom.domComputed((use) => {
// if (!use(this._isOpen)) { return null; } // remove line
const tool = use(this._extraTool);
```
```
private _buildHeaderDom() {
return dom.domComputed((use) => {
// if (!use(this._isOpen)) { return null; } // remove line
const tool = use(this._extraTool);
return tool ? this._buildToolHeader(tool) : this._buildStandardHeader();
```
Test Plan: Tested manually on desktop environnment with FF and chrome by shrinking the window.
Reviewers: paulfitz
Reviewed By: paulfitz
Differential Revision: https://phab.getgrist.com/D2710