Improve OSSA rauw capability and add unit tests

[atrick]

Make Ownership RAUW checks more precise - allows more optimization.
Allow RAUW to optimize struct_extract from function args
Add new CSE unit tests for OSSA optimization

CSE currently seems to be the easiest place to add tests for the RAUW utility.

[atrick]

@swift-ci test

[atrick]

The passes SCK testing locally with OME running before Mem2Reg

[atrick]

@swift-ci benchmark

[swift-ci]

Performance (x86_64): -O

Regression	OLD	NEW	DELTA	RATIO
StringFromLongWholeSubstring	4	5	+25.0%	0.80x
LessSubstringSubstring	39	43	+10.3%	0.91x (?)
DictionaryKeysContainsCocoa	33	36	+9.1%	0.92x (?)
String.replaceSubrange.ArrChar.Small	69	75	+8.7%	0.92x (?)
EqualSubstringSubstring	39	42	+7.7%	0.93x (?)
EqualStringSubstring	39	42	+7.7%	0.93x (?)
EqualSubstringString	39	42	+7.7%	0.93x (?)
Improvement	OLD	NEW	DELTA	RATIO
Breadcrumbs.MutatedUTF16ToIdx.Mixed	309	274	-11.3%	1.13x (?)
Breadcrumbs.MutatedIdxToUTF16.Mixed	313	279	-10.9%	1.12x (?)
StringBuilder	331	307	-7.3%	1.08x (?)
ConvertFloatingPoint.MockFloat64Exactly2	28	26	-7.1%	1.08x (?)

Code size: -O

Performance (x86_64): -Osize

Regression	OLD	NEW	DELTA	RATIO
LessSubstringSubstring	40	44	+10.0%	0.91x
EqualSubstringSubstringGenericEquatable	40	44	+10.0%	0.91x (?)
DictionaryKeysContainsCocoa	31	34	+9.7%	0.91x (?)
String.replaceSubrange.ArrChar.Small	69	75	+8.7%	0.92x
Improvement	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	6174	5674	-8.1%	1.09x (?)

Code size: -Osize

Performance (x86_64): -Onone

Improvement	OLD	NEW	DELTA	RATIO
UTF8Decode_InitFromBytes_ascii	359	299	-16.7%	1.20x (?)

Code size: -swiftlibs

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