fix!: Make publicDir and modulesDir relative to project root

[aklinker1]

BREAKING CHANGE: WXT's public/ and modules/ directories are now relative to the project root, not srcDir.

If you follow the default folder structure, this is not a breaking change.

If you set a custom srcDir, you have two options:

1. Keep the folders in the same place and your project config:

   // wxt.config.ts
   export defautl defineConfig({
     srcDir: "src",
   + publicDir: "src/public",
   + modulesDir: "src/modules",
   });

2. Leave your config as-is and move the your public/ and modules/ directories to the project root:

   + modules/
   + public/
     src/
         components/
         entrypoints/
   -     modules/
   -     public/
         utils/
     wxt.config.ts

---

This addresses #1209

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.17%. Comparing base (1db7377) to head (afd591e).
Report is 1 commits behind head on 0.20.0-breaking-changes.

Additional details and impacted files

@@                     Coverage Diff                     @@
##           0.20.0-breaking-changes    #1216      +/-   ##
===========================================================
+ Coverage                    79.99%   80.17%   +0.18%     
===========================================================
  Files                          124      124              
  Lines                         5928     5928              
  Branches                      1003     1002       -1     
===========================================================
+ Hits                          4742     4753      +11     
+ Misses                        1168     1157      -11     
  Partials                        18       18              

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