(@wdio/browser-runner): move assertions to Node.js environment

[christian-bromann]

Proposed changes

Currently we execute the expect-webdriverio library within the browser environment. However this has some drawbacks:

• it adds some load weight as all matcher files need to be loaded
• most importantly: it limits our capabilities for matchers as they have to support browser environments

In order to enable visual snapshot tests and DOM snapshot comparisons, we have to move out the assertion execution into the Node.js environment.

This patch makes the following changes:

• removes additional web socket server in favor for using Vite's HMR socket
• mocks out expect-webdriverio in the browser completely with fake matcher that redirect execution to the worker
• partial rewrite of the communication logic between browser and worker process
• support for custom command registration in Node.js

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Further comments

n/a

Reviewers: @webdriverio/project-committers