Deque#dup and #clone return the wrong type if subclassed

[HertzDevil]

I searched the 0.35.1 standard library docs and found that Deque also suffers from this same issue as Array (#9753) and Hash (#9754):

class Deque(T)
  def dup
    Deque(T).new(size) { |i| self[i].as(T) }
  end

  def clone
    Deque(T).new(size) { |i| self[i].clone.as(T) }
  end
end

The remaining types without a covariant #clone are Regex, String, and value types. They aren't meant to be subclassed so Deque is all that's left.

For #dup there is also OpenSSL::Digest, but likewise I believe that class shouldn't be subclassed.

[vlazar]

Probably both #9874 and #9753 shouldn't have community:newcomer labels.

I wanted to fix Deque#dup and Deque#clone how I did it in #9871 but it looks even worse than an issue appeared in #9753 (comment)

$ git diff
diff --git a/spec/std/deque_spec.cr b/spec/std/deque_spec.cr
index ea6d73052..2e2595294 100644
--- a/spec/std/deque_spec.cr
+++ b/spec/std/deque_spec.cr
@@ -36,6 +36,9 @@ end

 private alias RecursiveDeque = Deque(RecursiveDeque)

+private class DequeSubclass(T) < Deque(T)
+end
+
 describe "Deque" do
   describe "implementation" do
     it "works the same as array" do

ERROR:

$ bin/crystal spec spec/std/deque_spec.cr
Using compiled compiler at .build/crystal
Module validation failed: Function return type does not match operand type of return inst!
  ret i32* %1, !dbg !46
 %"Deque(/Users/vlazar/pet/PR/crystal/spec/std/deque_spec.cr::RecursiveDeque)"* (Exception)
  from src/llvm/module.cr:80:9 in 'verify'
  from src/compiler/crystal/codegen/codegen.cr:369:9 in 'finish'
  from src/compiler/crystal/codegen/codegen.cr:69:7 in 'codegen'
  from src/compiler/crystal/codegen/codegen.cr:65:5 in 'codegen:debug:single_module'
  from src/compiler/crystal/progress_tracker.cr:22:7 in 'codegen'
  from src/compiler/crystal/compiler.cr:172:16 in 'compile'
  from src/compiler/crystal/command/spec.cr:76:14 in 'spec'
  from src/compiler/crystal/command.cr:105:7 in 'run'
  from src/compiler/crystal/command.cr:49:5 in 'run'
  from src/compiler/crystal/command.cr:48:3 in 'run'
  from src/compiler/crystal.cr:11:1 in '__crystal_main'
  from src/crystal/main.cr:105:5 in 'main_user_code'
  from src/crystal/main.cr:91:7 in 'main'
  from src/crystal/main.cr:114:3 in 'main'
Error: you've found a bug in the Crystal compiler. Please open an issue, including source code that will allow us to reproduce the bug: https://github.com/crystal-lang/crystal/issues

[asterite]

Inheritance of generics types is broken. Please don't use it until it's fixed. And that's also a reason there's no need to change dup or clone, because they won't work well with generic inheritance