Andrew Jakubowicz

Add one hidden example for Labs/observers ResizeController usage

2

Note: For easier reviewing, I'm splitting out the labs/observers example playgrounds into isolated PRs. There will be a final PR that un-hides them. This change adds a small hidden `ResizeController`...

Create some samples showing how the `observers` labs package can be utilized. - [ ] ResizeController - https://github.com/lit/lit.dev/pull/970 - [ ] IntersectionController - https://github.com/lit/lit.dev/pull/977 - [ ] MutationController - [...

[infra] Fix "mkdir -p" breaking builds when on Windows

2

Fixes https://github.com/lit/lit/issues/3461 ### Why? `mkdir -p` [is not supported on Windows](https://github.com/npm/npm/issues/12774). The result of this, is that `mkdir` would create a `-p` directory on Windows and then crash when run...