Builder-Vite: use user's build.target

[Hoishin]

Closes #22223

What I did

If user has build.target in Vite config, use it for Storybook's Vite config.

How to test

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[valentinpalkovic]

Hi @Hoishin,

Thank you very much for this PR.

I don't feel very confident about merging this PR. This change could potentially cause the application to stop working. Therefore, since this is a potential breaking change, I would like to merge this PR for SB 8.0 after internal consultation.

Until then, the already mentioned workaround can be used:

async viteFinal(config) {
    return mergeConfig(config, {
      build: {
        target: 'esnext'
      },
    });
  },

I hope you understand our worries.

[IanVS]

This change could potentially cause the application to stop working.

@valentinpalkovic do you mean to say that storybook cannot be built with that target? Or when you say "cause the application to stop working", do you somehow mean the user's application itself?

I do agree that this is likely best left to 8.0, just curious if there are specific concerns about storybook being incompatible with different targets other than the default.

[valentinpalkovic]

@IanVS As far as I remember, we discussed this internally. We concluded that merging this PR could potentially break Storybook since the target might differ from the default one, and unexpected behavior might pop up. This is a precaution rather than basing the decision on some incidents in the past.

[IanVS]

since the target might differ from the default one

This makes sense, but on the other hand if Storybook is using a target that is different from the one specified in the user's vite config, I could also see that as being a bug, since their SB won't match their application. Personally I think it wouldn't be bad to release it before 8.0, but don't feel strongly one way or the other, especially since there's a pretty straightforward workaround.