(core) Minimazing widgets

Summary:
A feature that allows minimizing widgets on the ViewLayout.
- Code in ViewLayout and Layout hasn't been changed. Only some methods or variables were made public, and some events are now triggered when a section is dragged.
- Widgets can be collapsed or expanded (added back to the main area)
- Collapsed widgets can be expanded and shown as a popup
- Collapsed widgets support drugging, reordering, and transferring between the main and collapsed areas.

Test Plan: New test

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3779

app/common/gristUrls.ts

@@ -257,7 +257,7 @@ export function encodeUrl(gristConfig: Partial<GristLoadConfig>,
     queryParams[`${k}_`] = v;
   }
   const hashParts: string[] = [];
-  if (state.hash && state.hash.rowId) {
+  if (state.hash && (state.hash.rowId || state.hash.popup)) {
     const hash = state.hash;
     hashParts.push(state.hash?.popup ? 'a2' : `a1`);
     for (const key of ['sectionId', 'rowId', 'colRef'] as Array<keyof HashLink>) {