[BUG] anchor-name doesn't respect CSS cascade

[mmalerba]

Describe the bug
The anchor-name property doesn't respect the CSS cascade. For example:

.anchor {
  anchor-name: --name;
}
.anchor {
  anchor-name: --other-name;
}
.positioned {
  position: absolute;
  top: anchor(--name, bottom); // this should not anchor to `.anchor`, but currently does.
}

To Reproduce
I created a test demonstrating the issue here: main...mmalerba:css-anchor-positioning:cascade

Expected behavior
The anchor function should only match the anchor-name that is actually applied by the cascade

Additional context
This can be solved by shifting anchor-name into a custom property, but the custom property inherits by default, so we would either have to disable that with @property (potentially unacceptable due to browser support?) or just be careful to verify we're not reading inherited values. This is how I handled a similar issue for anchor-scope: 32f04d8 (#217)

[jgerigmeyer]

Good catch! I like the approach you used in #217, so that would be my leaning.

[jgerigmeyer]

I think this solution might also fix #212?