Fix panic when calling function that mutates itself

[dvtkrlbs]

Fixes #663

This commit fixes the panic when a function mutates itself. The issue happens since we borrow the object and when we call the statementList of the object we borrow_mut the object again to mutate it.
It changes the following:

• This adds a RcStatementList to cheaply clone StatementList
• It calls the run on the body of the function after dropping the first borrow by returning only the body after setting up the function local env

Thank you @HalidOdat for their help 😃

[codecov]

Codecov Report

Merging #667 into master will increase coverage by 0.03%.
The diff coverage is 92.59%.

@@            Coverage Diff             @@
##           master     #667      +/-   ##
==========================================
+ Coverage   73.14%   73.17%   +0.03%     
==========================================
  Files         192      193       +1     
  Lines       14005    14029      +24     
==========================================
+ Hits        10244    10266      +22     
- Misses       3761     3763       +2     

Impacted Files	Coverage Δ
boa/src/builtins/function/mod.rs	79.77% <ø> (ø)
boa/src/syntax/ast/node/mod.rs	20.51% <ø> (ø)
boa/src/syntax/ast/node/statement_list.rs	35.00% <75.00%> (+10.00%)	⬆️
boa/src/builtins/object/gcobject.rs	73.91% <91.66%> (+0.03%)	⬆️
boa/src/builtins/function/tests.rs	100.00% <100.00%> (ø)
boa/src/exec/mod.rs	67.83% <100.00%> (ø)

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[HalidOdat]

Also some tests showing that it does not panic any more and give the expected behaviour

[dvtkrlbs]

I added the test case from the issue

[dvtkrlbs]

Oh wait it should not return the edited value from the call statement. I have no idea why that happens. When we call a self mutating function somehow that mutated value leaks and gets returned from the function. It should not happen this way.

[HalidOdat]

Oh wait it should not return the edited value from the call statement. I have no idea why that happens. When we call a self mutating function somehow that mutated value leaks and gets returned from the function. It should not happen this way.

That is strange. does it happen on master too. if so then report an issue. this bug does not seem related to this PR

[dvtkrlbs]

>> function x() {}
undefined
>> function y() { x.y = 3 }
undefined
>> x.y
undefined
>> y()
3

happens on master too. so i will apply your suggestions and then this should be ready to merge since this issue is irrelevant to my pr

[dvtkrlbs]

Opened issue #672

[Razican]

Looks good to me :) Thanks for the fix!