Support flexible overlay size with connected position strategy

[jelbourn]

This issue tracks the high-level feature of supporting overlays that are automatically an appropriate size based on their position and viewport bounds. This is accomplished by creating a bounding container element that constrains the size of the overlay panel.

In-progress work is: https://github.com/jelbourn/material2/blob/better-connected-position/src/lib/core/overlay/position/better-connected-position-strategy.ts

[willshowell]

As a reminder from #8280 (comment), it would be great if whatever api is exposed for "position changes" emits on actual changes (instead of all position events) and within the ng zone.

[isaacplmann]

Is there work behind the scenes being done on this? Or is this something that would benefit from someone writing a PR?

@jelbourn, it looks like you've already put some thought into how to solve this. What is still left to be done?

[crisbeto]

The work is close to being finished @isaacplmann.

[isaacplmann]

@crisbeto Great! Glad to hear it. Thanks for the hard work.