[CSSWG][css-layout-api] FPWD of CSS Layout API L1

The CSS WG has published the First Public Working Draft of the CSS Layout
API Level 1:

https://www.w3.org/TR/css-layout-api-1/

This specification defines an API for performing layout on a box (element)
by being able to perform layout on children boxes, and positioning them.

There are a couple of demos of this API currently:
 - https://css-houdini.rocks/svg-path-layout
 -
https://googlechromelabs.github.io/houdini-samples/layout-worklet/masonry/
Both these demos his currently requires Chrome, with the "Experimental
Web Platform Features" flag turned on.

This is the first public WD defining this API. It defines how a web
developer can
register a layout, perform layout on children boxes by giving them
constraints,
read the CSS computed style of these boxes, and return information to the
engine about where the child layout results should be placed.

Please review the draft, and file any comments in the GitHub repository at:
    https://github.com/w3c/css-houdini-drafts/issues

For the CSS WG,
~Ian Kilpatrick