Web UI Polymer 3: Port cr-lazy-render

- Autogenerating Polymer 3 version of cr-lazy-render and test
- Adding to the demo page
- Removing legacy templatizer behavior from Polymer 3 exports, since it
should not be used now that cr-lazy-render is updated to use
Polymer.Templatize.templatize() instead (see
https://crrev.com/c/1786248).

Bug: 965770
Change-Id: I58b0cd8b19b6f668888aa48fc56c7ad9817efac1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1790641
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695810}