Refactor: Value::to_object to return GcObject

[RageKnify]

This Pull Request starts the work on #577.

It changes the following:

• Value::to_object now returns Result<GcObject> rather than Result<Value>
• Move Value::new_object_from_prototype to Object::new_object_from_prototype
• Minor changes in other files to accomodate the new API

I assume those minor changes will be cleaned up once the separation of the Object and Value API is complete.

[codecov]

Codecov Report

Merging #712 into master will increase coverage by 0.10%.
The diff coverage is 80.76%.

@@            Coverage Diff             @@
##           master     #712      +/-   ##
==========================================
+ Coverage   71.69%   71.79%   +0.10%     
==========================================
  Files         199      199              
  Lines       13865    13943      +78     
==========================================
+ Hits         9941    10011      +70     
- Misses       3924     3932       +8     

Impacted Files	Coverage Δ
boa/src/builtins/object/mod.rs	51.80% <60.00%> (+0.61%)	⬆️
boa/src/object/mod.rs	27.67% <80.00%> (+1.69%)	⬆️
boa/src/value/mod.rs	69.55% <81.81%> (-0.13%)	⬇️
boa/src/builtins/array/mod.rs	76.65% <100.00%> (ø)
boa/src/exec/call/mod.rs	72.41% <100.00%> (ø)
boa/src/exec/field/mod.rs	100.00% <100.00%> (ø)
boa/src/builtins/symbol/mod.rs	80.13% <0.00%> (-2.98%)	⬇️
boa/src/object/gcobject.rs	73.10% <0.00%> (-0.81%)	⬇️
boa/src/property/mod.rs	49.65% <0.00%> (-0.70%)	⬇️
boa/src/syntax/lexer/mod.rs	66.00% <0.00%> (-0.67%)	⬇️
... and 14 more

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[RageKnify]

There's one thing I started doubting after implementing, it may be more appropriate for the return type to be Object and then to wrap it in a GcObject only when required. What do you think @HalidOdat ?

[HalidOdat]

There's one thing I started doubting after implementing, it may be more appropriate for the return type to be Object and then to wrap it in a GcObject only when required. What do you think @HalidOdat ?

You mean new_object_from_prototype, right? I thick so too, but for .to_object it has to return GcObject
Also I think it's best to rename new_object_from_prototype to with_prototype so when we construct it its

let object = Object::with_prototype(Value::null(), ...);