fix: keep params in path overlay normalizer at the higher level

[domoritz]

Previously we moved the params into the layer but it seems like we should keep it at the higher level.

This fixes an issue that surfaced in #9253.

• Test that this works correctly with params and selection params

[keckelt]

How would I best test this? I re-built the examples with yarn build, yarn clean, and yarn build:examples on both the main branch and the PR branch to verify how the changes effect the produced chart. But they look the same on my machine:

main:

dom/rebuild-6782:

[domoritz]

The ci should have taken care of examples that are in the repo already. The question is whether the params should be in the first layer rather than at the outer spec level. The code looked intentional so I wanted to have someone else check.

[domoritz]

I think a good check is whether a deeply nested spec breaks with this change. And test selection params. I should do those.

[mattijn]

The intention of this PR is not exactly clear, but is the following issue + comment related here? #8230 (comment)

Also, when is this code invoked? I think this param lifting could be done in the section creating the extended vega-lite code.