refactor: cleanup event interface

[pi0]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Before releasing h3 1.8, this PR makes sure we minimize new interface changes and chances of future possible breaking changes.

Meanwhile, I was trying new Web APIs, and figured it is so easy to shoot in the foot by runtime expensive getters such as event.url or event.request (did myself ironically!). Composable utils are a little bit more verbose to use but also easy to replace or deprecate.

Changes from the last RC:

• Move event.rawBody to getRequestWebStream(event)
• Move event.request to toWebRequest(event)
• Move top-level web context to event.web? (WebEventContext = { request, url })
• Drop event._originalPath internal getter
• Drop event._hasBody internal getter
• Move event.url to getRequestURL(event)
• Fixed an unseen issue with readRawBody and readBody to support web request body streams
• Simplify getRequestPath to only normalize trailing double slashes
• Revert getRequestPath to 1.7.1 implementation and deprecate

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #506 (a798f6e) into main (588c8a3) will increase coverage by 0.03%.
The diff coverage is 88.28%.

@@            Coverage Diff             @@
##             main     #506      +/-   ##
==========================================
+ Coverage   82.40%   82.43%   +0.03%     
==========================================
  Files          31       31              
  Lines        3580     3604      +24     
  Branches      531      539       +8     
==========================================
+ Hits         2950     2971      +21     
- Misses        630      633       +3     

Files Changed	Coverage Δ
src/utils/proxy.ts	83.81% <50.00%> (ø)
src/adapters/plain.ts	79.35% <66.66%> (+0.13%)	⬆️
src/adapters/web.ts	94.82% <66.66%> (ø)
src/event/event.ts	86.61% <86.84%> (-1.96%)	⬇️
src/utils/request.ts	92.70% <90.47%> (-0.07%)	⬇️
src/utils/body.ts	94.55% <91.80%> (-0.91%)	⬇️