feat(html): Inline entry chunk into html when possible

[andylizi]

Description

This PR implements the solution described in #4554. Please see over there for details.

Additional context

About possible breakage: I've been doing some testing recently, looking through the plugin list in awesome-vite and such, and I haven't found any plugin that would be affected by this change. As for existing projects, I think most of them probably won't depend on the old behaviour.

Fixes #4554, fixes #3127, closes #3129.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[Shinigami92]

On the first look, it's LGTM.
But I'm not into deep technical aspects of this, so I would like to have another person to look deeper into the technical parts.

[patak-dev]

We discussed this feat with the team today and it looks good, and it is great that it also gives Vite Zero JS support. Thanks for this PR @andylizi, I think that @DylanPiercey and the marko team would be very happy to see this merged.

[patak-dev]

Thanks for implementing this feature @andylizi, we have merged this PR in preparations for vite 2.6-beta