[stdib] Audit @_fixed_layout on collection storage classes

[lorentey]

• Remove __SwiftNativeNSEnumerator from the ABI. (It’s only used in internal classes and in the Objective-C runtime.)
• Remove inlinability of init() and deinit for all the __SwiftNativeNSFoo superclasses except Array’s and Data’s.
• As an experiment, let’s try removing @_fixed_layout from _SetStorage and _DictionaryStorage. Their current ivars are all defined in their respective superclasses, so (if my mental model of how this works is correct), this will have little effect on benchmarks, but it adds a little bit of flexibility. Maybe.

[lorentey]

@swift-ci please test

[lorentey]

@swift-ci please benchmark

[swift-ci]

Build comment file:

Performance: -O

TEST	OLD	NEW	DELTA	RATIO
Improvement
NopDeinit	52623	45432	-13.7%	1.16x

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the
regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false
alarms. Unexpected regressions which are marked with '(?)' are probably noise.
If you see regressions which you cannot explain you can try to run the
benchmarks again. If regressions still show up, please consult with the
performance team (@eeckstein).

Hardware Overview

  Model Name: Mac Pro
  Model Identifier: MacPro6,1
  Processor Name: 12-Core Intel Xeon E5
  Processor Speed: 2.7 GHz
  Number of Processors: 1
  Total Number of Cores: 12
  L2 Cache (per Core): 256 KB
  L3 Cache: 30 MB
  Memory: 64 GB

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[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - ca09281

[swift-ci]

Build failed
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Git Sha - ca09281

[lorentey]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - ca09281

[jrose-apple]

@swift-ci Please test