[IMP] figure: add snap to figure drag & drop

With this commit, when moving/resizing a figure with the mouse the figure
will try to snap to other visible figures. This make it easy to align
figures together.

This is done in `figure.ts`. Where we added helpers to first drag the
figure, then helpers to snap the dragged figure.

"Snap lines" will be displayed to the user to visually see where the
snap is happening.

Odoo task 2907730

closes #1737

Signed-off-by: Lucas Lefèvre (lul) <lul@odoo.com>

src/components/figures/figure/figure.ts

@@ -59,7 +59,7 @@ css/*SCSS*/ `
     box-sizing: content-box;
 
     .o-fig-anchor {
-      z-index: ${ComponentsImportance.ChartAnchor};
+      z-index: ${ComponentsImportance.FigureAnchor};
       position: absolute;
       width: ${ANCHOR_SIZE}px;
       height: ${ANCHOR_SIZE}px;

src/components/figures/figure/figure.xml

@@ -7,6 +7,7 @@
         t-on-contextmenu.prevent.stop="onContextMenu"
         t-ref="figure"
         t-att-style="props.style"
+        t-att-data-id="props.figure.id"
         tabindex="0"
         t-on-keydown="(ev) => this.onKeyDown(ev)"
         t-on-keyup.stop="">