fix: type incompatibility with Vue 2.7 (fix #1993)

[deraw]

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
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Does this PR introduce a breaking change? (check one)

• Yes
• No

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• All tests are passing: https://github.com/vuejs/vue-test-utils/blob/dev/.github/CONTRIBUTING.md#development-setup
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Other information:

Fixes #1993

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[deraw]

I had to upgrade TypeScript to v4 since the types in vue/types/jsx.d.ts use index signature with template string pattern introduced in TypeScript 4.4.0.
However the tests are now broken and the issue will be resolved in Vue v2.7.9 since vuejs/vue#12727 has been merged.
I'm leaving this PR open until this version is released

[GrtDev]

2.7.9 has been released. Would be great to get this fix in so we can start using the vue-tsc for type checking 🙃

[yandongxu]

Vue 2.7.10
The typing issues are still there when using mount and shallowMount with defineComponent @GrtDev

[ColinRosati]

I have a solution for mount & shallowMount but I cant make a PR on this repo becuase Im on mac arm64 and some binareis arent supported, when installing the packages :(

We can add 2 overrides with the defineComponent api

export declare function mount<V extends Vue> (component: DefineComponent<V>, options?: ThisTypedMountOptions<V>): Wrapper<V>
export declare function shallowMount<V extends Vue> (component: DefineComponent<V>, options?: ThisTypedShallowMountOptions<V>): Wrapper<V>