Jest 27 support

[cexbrayat]

What problem does this feature solve?

The cli-plugin-unit-jest currently relies on jest v26, with vue-jest v5 for Vue 3 and v4 for Vue 2.
ts-jest v26 is used as well for TS projects.

A new package called vue3-jest has been introduced by the testing team to support Vue 3, with a versioning similar to what babel-jest and ts-jest do. An alpha release is available to support Jest v27 (vue3-jest@27.0.0-alpha.2 currently, see vuejs/vue-jest#343).

Even with this package, it's currently difficult to update to Jest v27, as the the plugin depends on jest 26 explicitly.
See vuejs/vue-jest#343 (comment) for a workaround using Yarn resolutions.

What does the proposed API look like?

The idea would be to:

• use vue3-jest@27 for Vue 3 (template and presets)
• make jest an explicit dependency of Vue projects, as it has been done for ts-jest and vue-jest, allowing to update the Jest version to v27
• bump babel-jest and ts-jest to v27 in the generated template

If that sounds good, I can try to work an PR, to hopefully land this in CLI v5

[haoqunjiang]

That would be cool!

Though, we need Jest 27 support for Vue 2, too, so that the generating logic could be simpler.

[cexbrayat]

@sodatea yeah I realized that, so I worked on a PR to land support for Vue 2 as well (vuejs/vue-jest#368)