Improved rendering order of nodes/edges in Graph View

[fbarl]

As a first step towards making #2431 work, we need to fix the rendering order of elements in <NodesChart />. The current order all edges -> all nodes doesn't look that bad as long as the background nodes are kept relatively transparent, but even so, on a closer look it can be seen how background nodes are rendered on top of foreground edges. This PR introduces a new rendering order:

• blurred edges
• blurred nodes
• normal edges
• normal nodes
• highlighted edges
• highlighted nodes
• hovered edges
• hovered nodes

Since SVG 1.1 doesn't support anything like CSS z-index, and SVG 2.0 standard still seems far away, the SVG rendering order necessarily corresponds to the DOM order, so I had to collapse both components <NodesChartNodes /> and <NodesChartEdges /> into <NodesChartElements /> to make the lists of nodes and edges intertwined.

No measurable performance loses were observed.

Now #2431 could be fixed e.g. by not making background nodes transparent, but changing their colors to similar effect.

[jpellizzari]

Implementation LGTM

[fbarl]

@jpellizzari I noticed later how the focused edges were blinking due to the CSS fading animation on them that was now being triggered on every hover with the changes I did. I added one more commit that fixes that by calculating edge thickness from <EdgeContainer /> and animating it through <Motion /> instead so PTAL at the behaviour before I merge it to make sure no new errors sneaked in.

[jpellizzari]

@fbarl Looks reasonably smooth with no problems. LGTM.