fix(ssr): renderToString cannot render comment

[clarkdo]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:
Fix nuxt/nuxt#4458

[posva]

Don't forget the test case 😄

[clarkdo]

@posva renderToString is using normalizeRender to create the compiler, but it doesn't pass comments parameter, so comments won't be renderered even after my pr.

But this pr can fix the scenario that component is loaded from vue-loader which is using comments attr to set the comments parameter.

[yyx990803]

We could have a test case that manually compiles the template with explicit comments options. A bit tedious but I think a test case is still needed.

[clarkdo]

Make sense, I’ll add one.

[clarkdo]

@yyx990803 @posva Test added.

[manniL]

Couldn't this lead to mismatch errors when comments are stripped on client-side? 🤔