[rubygems/rubygems] Raise a simpler error when RubyGems fails to activate a dependency

If you force uninstall a dependency but leave other gems depending on
it, those gems will fail to be activated.

In that case, RubyGems prints a rather complicated error:

```
$ rails --version
/Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1413:in 'block in Gem::Specification#activate_dependencies': Could not find 'activesupport' (= 8.0.1) among 478 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/Users/deivid/.local/share/gem/ruby/3.4.0:/Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/gems/3.4.0' at: /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/gems/3.4.0/specifications/railties-8.0.1.gemspec, execute `gem env` for more information
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1399:in 'Array#each'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1399:in 'Gem::Specification#activate_dependencies'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1381:in 'Gem::Specification#activate'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:283:in 'block in Gem.activate_bin_path'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:282:in 'Thread::Mutex#synchronize'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:282:in 'Gem.activate_bin_path'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/bin/rails:25:in '<main>'
/Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/dependency.rb:303:in 'Gem::Dependency#to_specs': Could not find 'activesupport' (= 8.0.1) - did find: [activesupport-7.1.3,activesupport-7.0.8.7] (Gem::MissingSpecVersionError)
Checked in 'GEM_PATH=/Users/deivid/.local/share/gem/ruby/3.4.0:/Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/gems/3.4.0' , execute `gem env` for more information
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1411:in 'block in Gem::Specification#activate_dependencies'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1399:in 'Array#each'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1399:in 'Gem::Specification#activate_dependencies'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1381:in 'Gem::Specification#activate'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:283:in 'block in Gem.activate_bin_path'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:282:in 'Thread::Mutex#synchronize'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:282:in 'Gem.activate_bin_path'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/bin/rails:25:in '<main>'
```

With this commit, the error becomes a bit simpler to parse:

```
$ rails --version
/Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1421:in 'block in Gem::Specification#activate_dependencies': Could not find 'activesupport' (= 8.0.1) among 478 total gem(s) (Gem::MissingSpecError)
Checked in 'GEM_PATH=/Users/deivid/.local/share/gem/ruby/3.4.0:/Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/gems/3.4.0' at: /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/gems/3.4.0/specifications/railties-8.0.1.gemspec, execute `gem env` for more information
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1407:in 'Array#each'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1407:in 'Gem::Specification#activate_dependencies'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems/specification.rb:1389:in 'Gem::Specification#activate'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:283:in 'block in Gem.activate_bin_path'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:282:in 'Thread::Mutex#synchronize'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/lib/ruby/site_ruby/3.4.0/rubygems.rb:282:in 'Gem.activate_bin_path'
	from /Users/deivid/.asdf/installs/ruby/3.4.1/bin/rails:25:in '<main>'
```

And also, we reduce exception based control flow in our code.

ruby/rubygems@7e48c49f2d

Author: deivid-rodriguez

lib/rubygems/specification.rb

@@ -1415,13 +1415,11 @@ def activate_dependencies
         raise e
       end
 
-      begin
-        specs = spec_dep.to_specs.uniq(&:full_name)
-      rescue Gem::MissingSpecError => e
-        raise Gem::MissingSpecError.new(e.name, e.requirement, "at: #{spec_file}")
-      end
+      specs = spec_dep.matching_specs(true).uniq(&:full_name)
 
-      if specs.size == 1
+      if specs.size == 0
+        raise Gem::MissingSpecError.new(spec_dep.name, spec_dep.requirement, "at: #{spec_file}")
+      elsif specs.size == 1
         specs.first.activate
       else
         name = spec_dep.name

test/rubygems/test_gem_specification.rb

@@ -652,6 +652,17 @@ def test_self_activate_conflict
     end
   end
 
+  def test_self_activate_missing_deps_does_not_raise_nested_exceptions
+    a = util_spec "a", "1.0", "b" => ">= 1.0"
+    install_specs a
+
+    e = assert_raise Gem::MissingSpecError do
+      a.activate
+    end
+
+    refute e.cause
+  end
+
   def test_self_all_equals
     a = util_spec "foo", "1", nil, "lib/foo.rb"