Projector Plugin: Bookmark loading is broken

[aknoerig]

Environment information (required)

I am using the standalone build of the projector plugin from master.

• bazel 2.1.0
• Chrome 85.0.4183.102

Issue description

In the projector plugin, the selected bookmark fails to load.

Steps to recreate:

1. Build the projector plugin using the standalone target
2. Open in browser
3. Switch to the "Word2Vec All" sample dataset
4. Select the sample bookmark "Politics: Bad to Good"

Console output:

Uncaught TypeError: evt.path[i].getAttribute is not a function
    at HTMLElement.getParentDataIndex (vz-projector-inspector-panel.mjs:404)
    at HTMLElement._radioButtonHandler (vz-projector-inspector-panel.mjs:377)
    at handler (apply-shim.js:264)
    at HTMLElement.<anonymous> (iron-a11y-keys-behavior.js:295)
    at _fire (dom-if.js:63)
    at trackForward (dom-if.js:444)
    at Object.click (dom-if.js:403)
    at HTMLElement._handleNative (dom-repeat.js:644)

Probably this is another side-effect of the recent upgrade to Polymer3?