feat(v2): allow hiding docs table of contents

[yangshun]

Motivation

I want to be able to hide the table of contents for Infima docs where the main content width is not wide enough. Example: https://facebookincubator.github.io/infima/docs/layout/grid

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Related PRs

(If this PR adds or changes functionality, please take some time to update the docs at https://github.com/facebook/docusaurus, and link to your PR here.)

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[endiliey]

How about accessing it in the UI through frontmatter instead ? Its very coupled to theme.

docusaurus/mdx-loader also exports frontmatter, and I think there isnt much server side processing done for it to be put in metadata

[endiliey]

In fact, I moved hide_title in my docs versioning PR which includes major performance gain on metadata processing. https://github.com/facebook/docusaurus/pull/1983/files

docusaurus/packages/docusaurus-theme-classic/src/theme/DocItem/index.js

Lines 66 to 68 in 31255ff

	const {
	frontMatter: {hide_title: hideTitle},
	} = DocContent;

Currently, our metadata has a lot of dynamic object construction like using delete.
Example:
In the below example, delete o.x does a lot more harm than good behind the scenes, as it changes o’s hidden class and makes it a generic slow object.

var o = { x: 1 };
delete o.x; // true
o.x; // undefined