<i18n dev> RFR: 8283996: Reduce cost of year and month calculations

[Claes Redestad]

A few integer divisions and multiplications can be replaced with test + addition, leading to a decent speed-up on java.time microbenchmarks such as `GetYearBench`. Numbers from my local x86 workstation, seeing similar speed-up on aarch64 and other x86 setups.

Baseline:

Benchmark                                            Mode  Cnt   Score   Error   Units
GetYearBench.getYearFromMillisZoneOffset            thrpt   15  18.492 ± 0.017  ops/ms
GetYearBench.getYearFromMillisZoneRegion            thrpt   15   6.121 ± 0.135  ops/ms
GetYearBench.getYearFromMillisZoneRegionNormalized  thrpt   15  18.936 ± 0.012  ops/ms
GetYearBench.getYearFromMillisZoneRegionUTC         thrpt   15   9.283 ± 0.222  ops/ms

Patched:

Benchmark                                            Mode  Cnt   Score   Error   Units
GetYearBench.getYearFromMillisZoneOffset            thrpt   15  20.931 ± 0.013  ops/ms
GetYearBench.getYearFromMillisZoneRegion            thrpt   15   6.858 ± 0.167  ops/ms
GetYearBench.getYearFromMillisZoneRegionNormalized  thrpt   15  20.923 ± 0.017  ops/ms
GetYearBench.getYearFromMillisZoneRegionUTC         thrpt   15  10.028 ± 0.182  ops/ms


Testing: java.time tests locally, CI tier1+2 ongoing.

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Commit messages:
 - Reduce cost of year and month calculations

Changes: https://git.openjdk.java.net/jdk/pull/8039/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8039&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283996
  Stats: 12 lines in 2 files changed: 6 ins; 1 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8039.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8039/head:pull/8039

PR: https://git.openjdk.java.net/jdk/pull/8039