Fix incorrect parent class assignment for Object and BasicObject

[st0012]

Motivation

When the Object and BasicObject classes are reopened, their parent class should remain BasicObject and nil respectively. This change fixes the current behaviour where the parent class is incorrectly set to Object.

The issue was discovered when pairing with @Morriar on #1046 as Object are displayed in Object's supertypes list too.

Implementation

We should check these 2 special cases before deciding the parent class.

Automated Tests

I added 4 new test cases for it.

Manual Tests

[st0012]

TIL: using arrays in case statement will allocate a new array each time the case statement is hit.

Script:

a = ["Object"]
b = ["Object"]
c = []

CONST = ["Object"]

def match_with_const(x)
  case x
  when CONST
    puts "Matched"
  end
end

def match_with_array(x)
  case x
  when ["Object"]
    puts "Matched"
  end
end

puts "Arrays count before match_with_const: #{ObjectSpace.count_objects[:T_ARRAY]}"
match_with_const a
match_with_const b
match_with_const c
puts "Arrays count after match_with_const: #{ObjectSpace.count_objects[:T_ARRAY]}"

puts "Arrays count before match_with_array: #{ObjectSpace.count_objects[:T_ARRAY]}"
match_with_array a
match_with_array b
match_with_array c
puts "Arrays count after match_with_array: #{ObjectSpace.count_objects[:T_ARRAY]}"

Output:

Arrays count before match_with_const: 1752
Matched
Matched
Arrays count after match_with_const: 1752
Arrays count before match_with_array: 1752
Matched
Matched
Arrays count after match_with_array: 1755