RFR: 8287292: Improve TransformKey to pack more kinds of transforms efficiently

[Claes Redestad]

The bespoke caching scheme in `jl.invoke.LambdaFormEditor.TransformKey` allows keys to be compacted when all byte values of the key fit in 4 bits, otherwise a byte array is allocated and used. This means that all transforms with a kind value above 15 will be forced to allocate and use array comparisons.

Removing unused and folding some transforms to ensure all existing kinds can fit snugly within the 0-15 value range realize a minor improvement to footprint, speed and allocation pressure of affected transforms, e.g. ~300bytes/op reduction in the `StringConcatFactoryBootstraps` microbenchmark:

Baseline:

Benchmark                                                      Mode  Cnt     Score     Error   Units
SCFB.makeConcatWithConstants                                   avgt   15  2048.475 ?  69.887   ns/op
SCFB.makeConcatWithConstants:?gc.alloc.rate.norm               avgt   15  3487.311 ?  80.385    B/op


Patched:

Benchmark                                                      Mode  Cnt     Score     Error   Units
SCFB.makeConcatWithConstants                                   avgt   15  1961.985 ? 101.519   ns/op
SCFB.makeConcatWithConstants:?gc.alloc.rate.norm               avgt   15  3156.478 ? 183.600    B/op

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Commit messages:
 - Revert unrelated and unverified hashCode change
 - Improve TransformKey to pack more kinds of transforms efficiently

Changes: https://git.openjdk.java.net/jdk/pull/8881/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8881&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287292
  Stats: 44 lines in 1 file changed: 21 ins; 10 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8881.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8881/head:pull/8881

PR: https://git.openjdk.java.net/jdk/pull/8881