fix(sfc): avoid to deindent when pad option is specified

[ktsn]

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:
I'm developing some editor extension which can highlight styles and noticed if there are root indentation, the highlight position is broken. I've found this is because vue-template-compiler deindents SFC contents even when pad option is specified.

I've changed this behavior to only deindent when pad option is not specified.

I have no idea why the template option is not padded but it would be needed to provide correct position of template block? If I'm missing something, please let me know.

[yyx990803]

@ktsn I've reverted this change due to this breaking some existing pug usage (#9169), but we will merge #7215 in 2.6 so that you can specify deindent: false to explicitly control this behavior.

[ktsn]

@yyx990803 I see. Thank you for letting me know!