RFR: 8343559: Optimize Class.getMethod(String, Class<?>...) for methods with no-arg

[jengebr]

This change optimizes the runtime of `Class.getMethod(String, Class<?>[])` in two ways:

1. While iterating across each Method to find a match (existing logic) it now compares parameter count before checking method name.  This check is substantially faster.
2. While iterating (existing logic) if the requested method has no arguments, the loop terminates early after finding one match.  This works because there can only be one zero-arg method with the matching name in the specific class.

A benchmark and unit tests are included; benchmark results (below) show an improvement in all cases, and an especially large gain when the immediate class contains the no-arg target.

Base:

Benchmark                          Mode  Cnt     Score    Error  Units
ClassGetMethod.getConcreteFiveArg  avgt    6    90.866 ±  2.698  ns/op
ClassGetMethod.getConcreteNoArg    avgt    6    72.472 ± 10.225  ns/op
ClassGetMethod.getIntfFiveArg      avgt    6   198.524 ±  7.089  ns/op
ClassGetMethod.getIntfNoArg        avgt    6   191.739 ±  4.695  ns/op
ClassGetMethod.getNoSuchMethod     avgt   10  2254.308 ± 42.829  ns/op
ClassGetMethod.getSuperFiveArg     avgt    6   165.897 ±  4.370  ns/op
ClassGetMethod.getSuperNoArg       avgt    6   148.361 ±  4.573  ns/op


Modified:

Benchmark                          Mode  Cnt     Score    Error  Units
ClassGetMethod.getConcreteFiveArg  avgt    6    77.059 ±  2.644  ns/op
ClassGetMethod.getConcreteNoArg    avgt    6    47.666 ±  6.544  ns/op
ClassGetMethod.getIntfFiveArg      avgt    6   164.427 ±  4.356  ns/op
ClassGetMethod.getIntfNoArg        avgt    6   161.256 ±  6.832  ns/op
ClassGetMethod.getNoSuchMethod     avgt   10  2158.844 ± 43.716  ns/op
ClassGetMethod.getSuperFiveArg     avgt    6   129.047 ±  4.414  ns/op
ClassGetMethod.getSuperNoArg       avgt    6   123.728 ±  6.182  ns/op

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Commit messages:
 - Adding copyright statements
 - 8343559: Optimize Class.getMethod(String, Class<?>...)

Changes: https://git.openjdk.org/jdk/pull/21929/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21929&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343559
  Stats: 404 lines in 3 files changed: 398 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/21929.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21929/head:pull/21929

PR: https://git.openjdk.org/jdk/pull/21929