[Breaking] `GetIntrinsic`: restrict intrinsic syntax

[ExE-Boss]

This makes it so that the intrinsic name has to either be enclosed by %, or the enclosing %‑signs must be omitted, but it’s invalid to include only one of them.

This also disallows dynamic property access, since it’s not allowed by the spec.

[ljharb]

OK, so it looks like the current behavior:

• accepts 'Array.prototype[push]', 'Array.prototype["push"]', 'Array.prototype[\'push\']': these are bugs and should be fixed in a patch, it should throw an exception
• throws on 'Array.prototype["push\']': this is correct, but could possibly use a better error message
• returns undefined for Array.prototype[anything with a . in it]: this is a bug and should be fixed in a patch; it should throw an exception
• would throw if the above bug is fixed for Array.prototype[%Symbol.iterator%], but this ideally should work.

I'd prefer to see this PR changed into a semver-patch to fix the first three items, and then in the future we can worry about the bracket intrinsic symbol syntax.

[ExE-Boss]

The code returns undefined because the !allowMissing && !(parts[i] in value) check is only performed when $gOPD is supported and i === parts.length - 1.

[codecov[bot]]

Codecov Report

Merging #102 into master will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #102      +/-   ##
==========================================
- Coverage   90.97%   90.97%   -0.01%     
==========================================
  Files         647      647              
  Lines        8931     8973      +42     
  Branches     2115     2124       +9     
==========================================
+ Hits         8125     8163      +38     
- Misses        806      810       +4     

Impacted Files	Coverage Δ
GetIntrinsic.js	96.74% <100.00%> (+1.25%)	:arrow_up:
2015/Set.js	92.30% <0.00%> (-2.70%)	:arrow_down:
2016/Set.js	92.30% <0.00%> (-2.70%)	:arrow_down:
2017/Set.js	92.30% <0.00%> (-2.70%)	:arrow_down:
2018/Set.js	92.30% <0.00%> (-2.70%)	:arrow_down:
2019/Set.js	92.30% <0.00%> (-2.70%)	:arrow_down:

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[ljharb]

I've pulled a few of these fixes into get-intrinsic (which has now been extracted to a separate package).

If all that would remain in this PR are the breaking changes, I think we can close this; if not, it'd be great to pull any remaining bugfixes into get-intrinsic.

[ljharb]

Closing with thanks; if there's any further problems or changes, please file them at https://github.com/ljharb/get-intrinsic