fix!: Make web-ext a peer dependency

[aklinker1]

Overview

Instead of hard switching to @wxt-dev/runner as in #1700, first make web-ext a peer dependency. Then it will be easy to add support for @wxt-dev/runner as a peer similar to web-ext without a breaking change, and give devs an easy path to migrate if they want.

• See updated docs for breaking changes.
• I updated the templates so new projects continue to open the browser during development by default.
• Move runner construction to resolveConfig, allowing modules to override the default and provide their own runner. Follows standards for construction of other objects on the wxt instance, like logger
• Update tests

Manual Testing

cd packages/wxt-demo

# Make sure the browser doesn't open automatically
pnpm rm web-ext
pnpm dev

# Make sure the browser does open automatically
pnpm add web-ext
pnpm dev

Related Issue

This PR closes #2078

[codecov]

Codecov Report

❌ Patch coverage is 73.91304% with 6 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (major@3cc44c5). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
packages/wxt/src/core/create-server.ts	57.14%	3 Missing ⚠️
packages/wxt/src/core/runners/web-ext.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             major    #2079   +/-   ##
========================================
  Coverage         ?   76.00%           
========================================
  Files            ?      112           
  Lines            ?     3046           
  Branches         ?      692           
========================================
  Hits             ?     2315           
  Misses           ?      647           
  Partials         ?       84           

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[aklinker1]

@PatrykKuniczak I'll add you as a reviewer once this is ready so you can see one of my PRs. Also if you have any feedback, please share!

[PatrykKuniczak]

LGTM

[github-actions]

Thanks for helping make WXT better!