feat(mocker): introduce @vitest/mocker package, allow { spy: true } instead of a factory

[sheremet-va]

Description

This PR introduces a way to spy on all exports instead of automocking the whole module by overriding every exported method with an empty function.

Closes #6099

import { method } from 'library'

vi.mock('library', { spy: true })

vi.isMockFunction(method) === true
method() // calls original method
expect(method).toHaveBeenCalled()

This is particularly useful in the browser mode where it is not possible to call spyOn on an import.

TODO:

• Docs
• More tests
• Browser support
• Refactor (there is currently a lot of duplicated logic between the browser and node, and logic for "behaviour" is similar to "type" in the browser)

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. If the feature is substantial or introduces breaking changes without a discussion, PR might be closed.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.

Tests

• Run the tests with pnpm test:ci.

Documentation

• If you introduce new functionality, document it. You can run documentation with pnpm run docs command.

Changesets

• Changes in changelog are generated from PR name. Please, make sure that it explains your changes in an understandable manner. Please, prefix changeset messages with feat:, fix:, perf:, docs:, or chore:.

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