feat(client): use visual routes

[Mister-Hope]

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[Mister-Hope]

This pr reduce outputsize and improves performance at the same time. by avoiding:

1. heavy operation with router.resolve

router.resolve performs RegExp.exec() when mapping the whole routes array to find a matched result.

2. duplicated route records with redirects and maps holding data, components, now a single map holds all pages info and pageKey is no longer used at client.

Breaking changes

• pageKey is removed at client, so operations like router.push(pageKey) router.resolve(pageKey) no longer work

• routeMeta is renamed to meta

  We want to decouple meta concept with router

  routeMeta is deprecated but still supported for backwards compatibility, we should remove the support in stable.

• People should use resolve in @vuepress/client to get page meta

  Getting page meta with router.resolve is deprecated but still supported for backwards compatibility, we should remove the support in stable. (We can support this for sure, but I think that decouple meta with routes could be better)

  Note: Calling router.resolve to get a correct page path is still supported as this is a correct usage. (but since it's heavy, maybe we should warn users to use resolve as first choice)

Other notes

To support clean url (e.g.: navigating to /a/b and resolve /a/b.html to /a/b), we improved generation of htmlRelativePath and htmlPath on Page object

[Mister-Hope]

Notes:

Since we use beforeResolve to align pageData with routePath, thie means router.resolve is still a heavy operation.

So we should avoid using router-link as it internally calls router.resolve to provide correct link on anchor tag. That is #1353 is still needed.

Though we no longer need RouterLink in that PR, VPLink should still be used by default in markdown and navbar, sidebar links.

[Mister-Hope]

@meteorlxy I prefer splitting the VPLink PR by updating the existing one #1353 after you merge this.

[Mister-Hope]

BTW, if we drop markdown link support, we can have higher performance here.

I would upvote to drop support for markdown links, since we already convert every markdown link in markdown files to <RouterLink> (or <VPLink> with VPLink pr).

At lease we can add an option here?

P.S: What do you think if we add a router field in config files with options like :

router: {
  cleanUrl: true,
  resolveMarkdownLink: true,
  // ...
}