feat: allow multi-browser configuration

[sheremet-va]

Description

Closes #5963
Closes #7017

The general idea is to inject new projects if instances are defined that inherit the same config and vite server

With this PR, browser.name and browser.providerOptions are deprecated. Use instances instead:

export default defineConfig({
  test: {
    browser: {
      provider: 'playwright',
      configs: [
        {
          browser: 'chromium',
          launch: { devtools: true },
        },
        {
          browser: 'firefox',
          setupFiles: ['./setup.firefox.ts'],
          provide: {
            secret: 'my-secret',
          },
        },
      ],
    }
  }
})

The main performance optimization here instead of using different projects is that we can reuse the same server and keep the cache.

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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[hi-ogawa]

Cool! I think I understood the idea and it makes sense to me 👍
I didn't check docs and there are some TODOs, but I guess those can be checked later.
Feel free to proceed if you want.