Initial support for metadata

[shuding]

This PR implements page and layout exported metadata field support with limited properties.

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• e2e tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have a helpful link attached, see contributing.md

[gnoff]

Going to continue to review but left a few comments for now that might be helpful

[gnoff]

We didn't specify the exact merging behavior of metadataBase but I provided a starting point that I think is correct. I'd like you to think about whether this is sensible and propose an alternative if you see problems with the approach

[gnoff]

This is a case where metadataBase should apply I believe. It is my understanding that urls in og tags need to be fully qualified. The logic maybe should be something like this

// this URL does not have a trailing slash but we should normalize it to assume it always ends in a "directory" not a "file" since we are going to extend it
baseURL = new URL("https://foo.example/base")
// normalize to directory
if (!baseURL.pathName.endsWith('/')) {
  baseURL.pathname = baseURL.pathname + '/';
}

url = new URL(urlStringOrURL, baseURL);

This should map the following

baseURL = new URL("https://foo.example/base")
"bar" => new URL("https://foo.example/base/bar")
"/bar" => new URL("https://foo.example/base/bar")
"./bar" => new URL("https://foo.example/base/bar")
"../bar" => new URL("https://foo.example/bar")
"https://bar.example/bar" => new URL("https://bar.example/bar")
new URL("https://bar.example/bar") => new URL("https://bar.example/bar")

[huozhi]

🙏 Will address the metadataBase in the following PRs! thanks for the details 👍

[gnoff]

I think you're basically there, just think you should get rid of the title cast since it is not necessary and may make future changes harder

[gnoff]

@huozhi @shuding The head.js implementation had some kind of integration into the router cache so that it would be updated as one would expect when transitioning from route to route. Does this need a similar kind of special case in the router?

cc @timneutkens you should probably give this a thumbs up from this perspective at least before we merge

[timneutkens]

cc @timneutkens you should probably give this a thumbs up from this perspective at least before we merge

Hopped on a call with @huozhi and added support for client-side navigation! All good from my side after Jiachi added the copy of the head.js tests that are passing 💯