Prevent Shadowenv from mutating BUNDLE_GEMFILE (#2874)

### Motivation

I finally understood the issue we were seeing of some folks requiring completely incompatible versions of add-ons.

If they used Shadowenv to override BUNDLE_GEMFILE, then it would cause the LSP to skip composing the bundle, which then leads to finding add-ons with `Gem.find_files` without having setup the bundle first.

That results in finding all `addon.rb` files defined by every installed gem, which might be ordered alphabetically and then results in requiring an old and incompatible Rails add-on version.

### Implementation

We cannot let Shadowenv override `BUNDLE_GEMFILE` because that fully messes up our entire composed bundle setup. I started deleting that key from the activated environment.

Author: vinistock

vscode/src/ruby/shadowenv.ts

@@ -32,6 +32,10 @@ export class Shadowenv extends VersionManager {
         `${shadowenvExec} exec -- ruby`,
       );
 
+      // Do not let Shadowenv change the BUNDLE_GEMFILE. The server has to be able to control this in order to properly
+      // set up the environment
+      delete parsedResult.env.BUNDLE_GEMFILE;
+
       return {
         env: { ...process.env, ...parsedResult.env },
         yjit: parsedResult.yjit,