refactor: remove temp page files and load page component via bundler (close #1584)

[meteorlxy]

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Provide a description in this PR that addresses what the PR is solving. If this PR is going to solve an existing issue, please reference the issue (e.g. close #123).

What is the purpose of this pull request?

• Bug fix
• New feature
• Documentation update
• Other
• Refactor

Description

Closes #1584

Changes:

• refactor: remove temp page files and load page component via bundler
• refactor(markdown): remove relativePathPrefix option from assetsPlugin
• feat: support importing module via relative paths in page files
• feat: support importing markdown as vue component

TODOs

• HMR
• Refactor dev watcher, update pages & pagesMap
• Watch page deps and invalidate the cache

[coveralls]

Pull Request Test Coverage Report for Build 16794974048

Details

• 36 of 59 (61.02%) changed or added relevant lines in 13 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-1.2%) to 73.229%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/cli/src/commands/dev/handlePageUnlink.ts	0	1	0.0%
packages/core/src/app/appPrepare.ts	0	1	0.0%
packages/cli/src/commands/dev/handlePageAdd.ts	0	2	0.0%
packages/cli/src/commands/dev/handlePageChange.ts	0	2	0.0%
packages/core/src/app/prepare/preparePageChunk.ts	0	2	0.0%
packages/core/src/page/renderPageToVue.ts	19	34	55.88%

Totals
Change from base Build 16794961355:	-1.2%
Covered Lines:	698
Relevant Lines:	945

---

💛 - Coveralls

[Mister-Hope]

The ecosystem and downstream plugins need a new option, I would design it as onPageUpdate

Technically speaking, a plugin can get all pages in onInitialized lifecycle, but when a new page is added, changed or removed in devServer, a plugin cannot subscribe because page generating and extendsPage hook are all async, we are watching the temp files before this PR, but this workaround no longer works now.

So to let the plugin work well, the onPageUpdate should be:

onPageUpdated(app: App, type: 'add' | 'change' | 'remove', oldPage: Page | null, newPage: Page | null)

Or we can split it into 3 subscriber:

onPageAdded(app: App, newPage: Page | null)
onPageChanged(app: App, oldPage: Page, newPage: Page)
onPageRemoved(app: App, oldPage: Page)