perf: avoid execSync on openBrowser

[patak-dev]

Description

openBrowser was blocking the node thread in OSX, this PR saves a bit of time by using exec instead. We don't really use the return value of openBrowser.

On M1, I'm getting ~200ms faster start after this PR

If --open is used, frameworks could trigger a transformRequest of the app entry point so the modules are already pre-processed when the browser finally opens and starts to request them. We could also try to add a cache to transformIndexHtml so we start right away for apps that have an index.html by default.

@ArnaudBarre could you check this, maybe there was another reason to make these sync.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[ArnaudBarre]

LGTM

The fact that it was blocking was not a big deal for me because almost nothing happens while the browser is opening. But that's a good idea to "simulate" a / get so that the transformRequest jobs starts sooner (this should be done in parallel of the open browser call)

[bluwy]

Awesome!