feat!: Run a WebView per Snap on mobile

[FrederikBolding]

Allows us to run Snaps locally on mobile by instantiating a WebView per Snap. This PR changes the WebViewExecutionService to let it instantiate and remove webviews (this will need support on the mobile implementation side). Additionally alters the WebView bundle so it no longer functions as a "proxy executor", but instead inherits from the iframe executor implementation.

Breaking changes

• WebViewExecutionService now requires createWebView and removeWebView constructor arguments, getWebView is no longer supported.
• The WebView bundle in snaps-execution-environments no longer supports proxy executor calls and functions as a single executor.

[codecov]

Codecov Report

Attention: Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.

Project coverage is 94.90%. Comparing base (d7e2167) to head (2a04db7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../snaps-execution-environments/src/webview/index.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3085      +/-   ##
==========================================
+ Coverage   94.88%   94.90%   +0.01%     
==========================================
  Files         506      506              
  Lines       11121    11119       -2     
  Branches     1709     1709              
==========================================
  Hits        10552    10552              
+ Misses        569      567       -2     

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