[stdlib] Expunge FixedArray from ABI

[milseman]

No description provided.

[milseman]

@swift-ci please benchmark

[milseman]

@swift-ci please smoke test

[swift-ci]

Build comment file:

Performance: -Onone

TEST	OLD	NEW	DELTA	RATIO
Regression
DropFirstArrayLazy	31975	35208	+10.1%	0.91x
PrefixArrayLazy	31857	35032	+10.0%	0.91x
DropLastArrayLazy	10638	11696	+9.9%	0.91x
SuffixArrayLazy	10629	11599	+9.1%	0.92x

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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