Add support for configurable jsxImportSource when using Emotion SWC

[JohnDaly]

Describe the feature you'd like to request

Currently, when opting into the SWC Emotion plugin, there is an assumption made that the jsxImportSource is @emotion/react. This prevents projects that use Emotion 10 from being able to use SWC, because the package which provides the JSX runtime is called @emotion/core.

Describe the solution you'd like

I have a couple suggestions for how to resolve this.

1. Allow the jsxImportSource from jsConfig.compilerOptions to be used, if present
2. Allow a jsxImportSource to be specified as part of the emotion SWC options

Of these two suggestions, I think the first one is probably the better way to go, since its a little surprising that the jsxImportSource from jsConfig.compilerOptions is ignored if the nextConfig.experimental.emotion option is set

Describe alternatives you've considered

I'm not aware of another way to set the jsxImportSource to support @emotion/corewhile using the SWC Emotion plugin