Fix panics from multiple borrows of Map.

[joshwd36]

This Pull Request fixes/closes #1058.

It changes the following:

• Move to an index-based approach to iterating during for-each.

This approach still has issues, as mentioned in #1058 (comment)

[codecov]

Codecov Report

Merging #1077 (49a172c) into master (5a5061c) will decrease coverage by 0.01%.
The diff coverage is 70.00%.

@@            Coverage Diff             @@
##           master    #1077      +/-   ##
==========================================
- Coverage   58.70%   58.68%   -0.02%     
==========================================
  Files         176      176              
  Lines       12391    12405      +14     
==========================================
+ Hits         7274     7280       +6     
- Misses       5117     5125       +8     

Impacted Files	Coverage Δ
boa/src/builtins/map/mod.rs	71.08% <70.00%> (-1.29%)	⬇️
boa/src/builtins/map/ordered_map.rs	57.57% <0.00%> (-6.07%)	⬇️

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[Razican]

Test262 conformance changes:

Test result	master count	PR count	difference
Total	78,497	78,497	0
Passed	24,805	24,813	+8
Ignored	15,587	15,587	0
Failed	38,105	38,097	-8
Panics	26	20	-6
Conformance	31.60	31.61	+0.01%

[RageKnify]

Seems like a good solution to the panics.
This is a pretty weird part of the spec, certain callbacks can create infinite-loops:

function callingCallback(value, key, map) {
  console.log(key)
  map.delete(key)
  map.set(key, value)
}

Not sure how to implement this, might want to look at other engines' implementations.

[tofpie]

This looks good to me. Thanks.