[css] Support "speak" property

[ryanaltvater]

VS Code version:
1.81.1

OS version:
macOS Ventura 13.4.1

Steps to reproduce:

1. Use speak attribute within scss files

Warning message:
Unknown property: "speak" scss(unknownProperties)

Duplicate issues (closed):
#43022
#61719

Resources:
https://www.w3.org/TR/css-speech-1/#speaking-props-speak
stylelint/stylelint#3285 (comment)
mdn/data#218
https://github.com/Microsoft/vscode-css-languageservice/blob/master/src/data/browsers.ts
https://github.com/mdn/data/blob/master/css/properties.json

Does this issue occur when all extensions are disabled?
Yes

I realize that the specification was abandoned at one point (2018), but it appears to have been revived as of February this year. It is currently in draft, and so I'm just capturing all of this so that it doesn't get overlooked. Appears that only Chrome supports speak at the moment, and Safari supports speak-as. Firefox hasn't jumped into the game yet.

[aeschli]

We're getting the list of valid properties from mdn. Waiting for it to appear there (as well as most browsers to adopt it).
In the meantime, if you don't want to see the warning you can manually add the property to setting css.lint.validProperties

[shadow-identity]

Hi @aeschli, I found that VSCode reports string-set property as unknown, and I wanted to make a pull request, but then I found that this property exist in css.cson, and now I'm confused, why VS Code reports it? Doesn't it use css.cson anymore?

[aeschli]

https://github.com/microsoft/vscode-css/blob/main/grammars/css.cson is only for syntax highlighing.
For code completion and hover, we extract properties and at rules from MDN.
This is done in in the repo https://github.com/microsoft/vscode-custom-data.