RFR: 8285633: Take better advantage of generic MethodType cache

[Claes Redestad]

The `MethodType.genericMethodType` methods provide convenience methods for certain common method types and also provide `@Stable` cache that allows for constant folding. This patch enhances the more generic `methodType` methods to take advantage of this cache, when possible. This allows calls like `MethodType.methodType(Object.class, Object.class, ...)` to constant fold, making them 50x+ faster and allocation-free.

Baseline:

Benchmark                                    Mode  Cnt   Score   Error  Units
MethodTypeAcquire.baselineRaw                avgt    5   0.673 ? 0.036  ns/op
MethodTypeAcquire.testGenericObject          avgt    5   0.520 ? 0.162  ns/op
MethodTypeAcquire.testMultiPType             avgt    5  47.922 ? 1.778  ns/op
MethodTypeAcquire.testMultiPType_Arg         avgt    5  28.992 ? 0.949  ns/op
MethodTypeAcquire.testMultiPType_ObjectAndA  avgt    5  56.698 ? 0.879  ns/op
MethodTypeAcquire.testMultiPType_ObjectOnly  avgt    5  55.705 ? 0.854  ns/op
MethodTypeAcquire.testObjectObject           avgt    5  31.729 ? 2.204  ns/op
MethodTypeAcquire.testReturnInt              avgt    5  26.171 ? 0.141  ns/op
MethodTypeAcquire.testReturnObject           avgt    5  24.340 ? 0.868  ns/op
MethodTypeAcquire.testReturnVoid             avgt    5  24.793 ? 2.816  ns/op
MethodTypeAcquire.testSinglePType            avgt    5  32.653 ? 1.082  ns/op


Patched:

Benchmark                                    Mode  Cnt   Score   Error  Units
MethodTypeAcquire.baselineRaw                avgt    5   0.727 ? 0.382  ns/op
MethodTypeAcquire.testGenericObject          avgt    5   0.658 ? 0.655  ns/op
MethodTypeAcquire.testMultiPType             avgt    5  48.066 ? 1.187  ns/op
MethodTypeAcquire.testMultiPType_Arg         avgt    5  27.097 ? 0.745  ns/op
MethodTypeAcquire.testMultiPType_ObjectAndA  avgt    5  58.074 ? 6.299  ns/op
MethodTypeAcquire.testMultiPType_ObjectOnly  avgt    5   0.538 ? 0.195  ns/op
MethodTypeAcquire.testObjectObject           avgt    5   0.520 ? 0.162  ns/op
MethodTypeAcquire.testReturnInt              avgt    5  28.093 ? 0.235  ns/op
MethodTypeAcquire.testReturnObject           avgt    5   0.540 ? 0.204  ns/op
MethodTypeAcquire.testReturnVoid             avgt    5  24.746 ? 0.706  ns/op
MethodTypeAcquire.testSinglePType            avgt    5  32.662 ? 1.924  ns/op


The cost on method types that don't match are in the noise (0-2ns/op). Even on a test I constructed to act as a worst case (`testMultiPType_ObjectAndA`) there's barely any appreciable cost.

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Commit messages:
 - Copyrights
 - 8285633: Take better advantage of generic MethodType cache

Changes: https://git.openjdk.java.net/jdk/pull/8398/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8398&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285633
  Stats: 101 lines in 8 files changed: 78 ins; 1 del; 22 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8398.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8398/head:pull/8398

PR: https://git.openjdk.java.net/jdk/pull/8398