Make it clearer Opal is used on https://try.ruby-lang.org/

[eregon]

On https://try.ruby-lang.org/playground/ it is clear that Opal is the default, and one can choose CRuby.

But on the homepage, https://try.ruby-lang.org/ says nothing that Opal is used, and CRuby cannot be chosen.

This leads to confusion, e.g.:

• https://bugs.ruby-lang.org/issues/18609#note-7
• Different behavior between TryRuby and MRI #78 (comment)

I think the best would be for the homepage to also have the "engine selector" (Opal/CRuby), so the homepage would be like the Playground page (but still without the docs)

[eregon]

I believe this is a severe problem, people think https://try.ruby-lang.org/ is Ruby (= standard Ruby = CRuby) but it's Opal and it's incompatible in many ways. Here is a real life example which wasted hours of work due to this: oracle/truffleruby#2905 (comment)

I think the best way to change this is to default to CRuby, and barring that to make extremely clear it's Opal and not CRuby.
I have nothing against Opal, but this leads to a lot of confusion.

[eregon]

#134 seems another clear reason why Opal shouldn't be the default.
The Ruby programming language has a strong difference between Integer and Float.
Opal doesn't have that because JS doesn't have that, but the default playground should clearly respect this essential property of the Ruby language.