Add require: "debug/prelude" after debug's Gemfile entry

In ruby/debug#797, we found that requiring
`debug` automatically activates it, which could introduce runtime overhead
and cause memory bloat. And I think many users aren't aware of this and
could be taxed by this unnecessarily (e.g. having longer builds on CI).

Therefore, I propose to add `require: "debug/prelude"` after `debug`'s
Gemfile entry in the default Gemfile template. This way, users can
still use breakpoint methods like `debugger`, `binding.break`, and `binding.b`,
but the debugger won't be activated until a breakpoint is hit.

Author: st0012

railties/CHANGELOG.md

@@ -1,3 +1,14 @@
+*   Generated Gemfile will include `require: "debug/prelude"` for the `debug` gem
+
+    Requiring `debug` gem directly automatically activates it, which could introduce
+    additional overhead and memory usage even without entering a debugging session.
+
+    By making Bundler require `debug/prelude` instead, developers can keep their access
+    to breakpoint methods like `debugger` or `binding.break`, but the debugger won't be
+    activated until a breakpoint is hit.
+
+    *Stan Lo*
+
 *   Allow Actionable Errors encountered when running tests to be retried.
 
     ```txt

railties/lib/rails/generators/rails/app/templates/Gemfile.tt

@@ -33,7 +33,7 @@ gem "bootsnap", require: false
 
 group :development, :test do
   # See https://guides.rubyonrails.org/debugging_rails_applications.html#debugging-with-the-debug-gem
-  gem "debug", platforms: %i[ mri <%= bundler_windows_platforms %> ]
+  gem "debug", platforms: %i[ mri <%= bundler_windows_platforms %> ], require: "debug/prelude"
 <%- unless options.skip_brakeman? -%>
 
   # Static analysis for security vulnerabilities [https://brakemanscanner.org/]