feat(client): use visual routes

[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