Validate user input encoding

If the user has the encoding of her system messed up, she may end up
sending us incorrectly encoding input, causing "invalid byte sequence in
UTF-8" errors at random places.

These errors can be forced on a system without encoding issues with
something like:

```
$ gem install$(echo -e "\xFF") foo
/Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/config_file.rb:534:in `block in set_config_file_name': invalid byte sequence in UTF-8 (ArgumentError)
	from /Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/config_file.rb:530:in `each'
	from /Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/config_file.rb:530:in `set_config_file_name'
	from /Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/config_file.rb:177:in `initialize'
	from /Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/gem_runner.rb:71:in `new'
	from /Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/gem_runner.rb:71:in `do_configuration'
	from /Users/deivid/.asdf/installs/ruby/3.2.1/lib/ruby/site_ruby/3.2.0/rubygems/gem_runner.rb:33:in `run'
	from /Users/deivid/.asdf/installs/ruby/3.2.1/bin/gem:10:in `<main>'
```

This commit makes RubyGems print a better error in this case:

```
$ ruby -Ilib bin/gem install$(echo -e "\xFF") foo
/Users/deivid/Code/rubygems/rubygems/lib/rubygems/gem_runner.rb:75:in `validate_encoding': invalid argument: 'install�' has invalid encoding (Gem::OptionParser::InvalidArgument)
	from /Users/deivid/Code/rubygems/rubygems/lib/rubygems/gem_runner.rb:31:in `run'
	from bin/gem:10:in `<main>'
```

Author: deivid-rodriguez

lib/rubygems/gem_runner.rb

@@ -29,6 +29,7 @@ def initialize
   # Run the gem command with the following arguments.
 
   def run(args)
+    validate_encoding args
     build_args = extract_build_args args
 
     do_configuration args
@@ -72,6 +73,14 @@ def extract_build_args(args) # :nodoc:
 
   private
 
+  def validate_encoding(args)
+    invalid_arg = args.find {|arg| !arg.valid_encoding? }
+
+    if invalid_arg
+      raise Gem::OptionParser::InvalidArgument.new("'#{invalid_arg.scrub}' has invalid encoding")
+    end
+  end
+
   def do_configuration(args)
     Gem.configuration = @config_file_class.new(args)
     Gem.use_paths Gem.configuration[:gemhome], Gem.configuration[:gempath]

test/rubygems/test_gem_gem_runner.rb

@@ -54,6 +54,12 @@ def test_do_configuration
     assert_equal %w[--commands], Gem::Command.extra_args
   end
 
+  def test_validate_encoding
+    assert_raise Gem::OptionParser::InvalidArgument do
+      @runner.run(["install\xFF", "foo"])
+    end
+  end
+
   def test_extract_build_args
     args = %w[]
     assert_equal [], @runner.extract_build_args(args)