Fix Incorrect links in "vscode namespace API" Doc

[anantoghosh]

In description for ExtensionContext -> storagePath, links to globalState and workspaceState are incorrect and lead to an error page.

[mention-bot]

@anantoghosh, thanks for your PR! By analyzing the history of the files in this pull request, we identified @jrieken, @egamma and @alexandrudima to be potential reviewers.

[msftclas]

Hi @anantoghosh, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

This seems like a small (but important) contribution, so no Contribution License Agreement is required at this point. Real humans will now evaluate your PR.

TTYL, MSBOT;

[jrieken]

Thanks!