fix for ember 4

[luxzeitlos]

This is a try to fix compatibility with ember 4. Especially this removes @ember/legacy-built-in-components.
For this I basically completely changed the special <LinkTo component to not extend the built-in component but instead proxy it.

[nickschot]

This addon (legacy-built-in-components) should be compatible with ember 4 (and appears to be from current state of master). We will need to implement some kind of replacement, but I'm not sure yet if I want it to be:

• this
• a modifier the user can apply
• simply the current close action and we update the docs that the user can use the {{on "click"}} modifier to call the close action