feat(v2): add site title to meta title

[lex111]

Motivation

Resolves https://docusaurus.canny.io/admin/board/feature-requests/p/allow-browser-tab-title-to-have-a-prefix

Bcause this is the expected behavior (especially since it was in v1) - the site name is usually contained in the title itself and this is suitable for most websites (+ better for SEO).

The only thing I'm not sure about existing a tagline in the case when the title is not set, in v1 there was even a separate config parameter (disableTitleTagline) that removes the tagline from the final meta title, but I do not think it is a good idea to implement it in v2.

docusaurus/packages/docusaurus-1.x/lib/core/Site.js

Lines 38 to 42 in 7e60a28

	const title = this.props.title
	? `${this.props.title} · ${this.props.config.title}`
	: (!this.props.config.disableTitleTagline &&
	`${this.props.config.title} · ${tagline}`) ||
	this.props.config.title;

Maybe then do not include the tagline in the meta title, after all, this is typical only for the home page, for other pages without a title it is better to just use site title (IMO).

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

Make sure site title is included in meta title (docs/blog/pages).

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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[yangshun]

LGTM. Can we change to either - or |? Self-merge

[yangshun]

I think using - or | will be better

[lex111]

@yangshun done, but what about avoiding to use tagline if there is no title? I mentioned this in the PR description.

${siteTitle} · ${tagline} -> ${siteTitle}

Instead, use tagline only on the home page.

[yangshun]

Agreed. Don't use tagline elsewhere. I think if the tagline is too long it even looks weird to have it as the <title> on the homepage, just like ours :S

[lex111]

Excluded tagline from meta title of any page, but bring back it to title on home page.