Add contributes.html.customTags and contributes.html.customAttributes

[octref]

Continuation of #62976.

These contribution points should be similar to the user configurations:

{
  "html.experimental.custom.tags": [
    "./web-components.json",
    "./element-details/web-components.json"
  ],
  "html.experimental.custom.attributes": [
    "./web-component-attributes.json"
  ]
}

They allow extension authors to publish a list of tags / attributes together with its frameworks, and VS Code could load them for HTML language features.

[octref]

We are shipping this instead:

"contributes": {
	"html": {
		"customData": [
			"./data/svg-html-contribution.json"
		]
	},
}