[stdlib] Add 256 bits of extra state to Hasher

[lorentey]

This is the ugly part of #20185, without anysome of the ABI cleanups.

The original PR also removed the _HasherCore protocol, but that leads to code size and performance regressions due to overenthusiastic inlining. (See #20198)

[lorentey]

@swift-ci please benchmark

[swift-ci]

Build comment file:

Code size: -O

TEST	OLD	NEW	DELTA	RATIO
Regression
DictionarySwap.o	27430	27894	+1.7%	0.98x
DictTest4Legacy.o	26936	27384	+1.7%	0.98x
DictTest4.o	26046	26430	+1.5%	0.99x

Code size: -Osize

TEST	OLD	NEW	DELTA	RATIO
Regression
DictTest4.o	21199	21535	+1.6%	0.98x
DictTest4Legacy.o	22585	22905	+1.4%	0.99x

Performance: -Onone

TEST	OLD	NEW	DELTA	RATIO
Improvement
Histogram	6844	5753	-15.9%	1.19x
RGBHistogram	24335	21601	-11.2%	1.13x

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: 16 GB

---

[lorentey]

@swift-ci please smoke test and merge

[lorentey]

@swift-ci please smoke test and merge