Allow `force_ruby_platform` to apply only to some platforms

Describe the problem as clearly as you can

We have this in our Gemfile:

gem 'grpc', force_ruby_platform: RUBY_PLATFORM =~ /arm64-darwin/

and our platforms are:

PLATFORMS
  arm64-darwin-21
  x86_64-darwin-21
  x86_64-linux

We need to do this because the grpc gem doesn't work on Apple M1 Macbooks unless you compile the gem yourself (hence the force_ruby_platform. Additionally, we do this so that our peers on Apple Intel Macbooks don't have to compile the gem since it can take a very long time to compile on Intel machines.

The problem is that depending on who runs a bundle update ..., the Gemfile.lock changes. Here's a breakdown:

If Gemfile.lock was created from scratch by an M1, it'll look like this:
M1:

     grpc (1.43.1)
       google-protobuf (~> 3.18)
       googleapis-common-protos-types (~> 1.0)

Which means Intel machines will compile (😞). Additionally, if an Intel does a bundle update ... it doesn't add extra platforms.

If Gemfile.lock was created from scratch by an Intel, it'll look like this:
Intel:

     grpc (1.43.1)
       google-protobuf (~> 3.18)
       googleapis-common-protos-types (~> 1.0)
     grpc (1.43.1-x86_64-darwin)
       google-protobuf (~> 3.18)
       googleapis-common-protos-types (~> 1.0)
     grpc (1.43.1-x86_64-linux)
       google-protobuf (~> 3.18)
       googleapis-common-protos-types (~> 1.0)

Which means it works perfectly for both Intel and M1. However, if an M1 does a bundle update, it will remove the extra platforms so that the Gemfile.lock looks like it was generated by an M1 from scratch.

Maybe this is the intended behavior, but it causes a lot of confusion. But it also seems inconsistent for bundle update. Any advice would be appreciated.

Start with the Gemfile and Gemfile.lock examples, then reproduce the behavior on arm64-darwin and x86_64-darwin using bundle update. Trace how force_ruby_platform and platform entries are handled during dependency resolution. Done should mean updates preserve the appropriate platform-specific gems while forcing the Ruby platform only where requested.