fix(overlays): fix memory leaks of adopt-styles and OverlayMixin (#2300)

[riovir]

What I did

1. Adjust the adopt-style styleCache to be a WeakMap preventing the renderRoots from being garbage collected
2. Let the OverlayMixin unwire its OverlayController from the OverlayManager on teardown

[changeset-bot]

🦋 Changeset detected

Latest commit: 5e95cc0

The changes in this PR will be included in the next version bump.

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@lion/ui	Patch

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[riovir]

Will need to look closer into how to keep the OverlayController reference in the OverlayManager without never releasing it. Weak collections seem to be a no-go, as iteration is required. I'm hoping that carefully cutting and restoring the references in the connected / disconnected or init / teardown hooks will get the right results without introducing regression.

[Sciurus7]

That is looking good!
It would be much appreciated if this PR could be handled and released relatively quickly. My company is working on a framework where this memory leak will wreak havoc unless fixed. Unfortunately it is nigh impossible to implement some temporary workaround in our own components that would apply the same fixes as this PR, so we are really dependent on this being fixed in Lion.