<i18n dev> RFR: 8278642: Refactor java.util.Formatter

[Claes Redestad]

A few refactorings to how `java.util.Formatter` sets up `FormatString`s, aligning the implementation with changes explored by the TemplatedStrings JEP and ever so slightly improving performance:

- turn `Flags` into an `int` (fewer allocations in the complex case)
- remove some superfluous varargs: `checkBadFlags(Flags.PARENTHESES, ...` -> `checkBadFlags(Flags.Parentheses | ...` - again less allocations in the complex cases since these varargs arrays were being allocated. Also improves error messages since all bad flags will be listed in the exception message.
- make `FormatSpecifier` and `FixedString` static, reducing size of these objects slightly.

Baseline: 

Benchmark                                                           Mode  Cnt     Score     Error   Units
StringFormat.complexFormat                                          avgt   25  8977.043 ± 246.810   ns/op
StringFormat.complexFormat:·gc.alloc.rate.norm                      avgt   25  2144.170 ±   0.012    B/op
StringFormat.stringFormat                                           avgt   25   252.109 ±   2.732   ns/op
StringFormat.stringFormat:·gc.alloc.rate.norm                       avgt   25   256.019 ±   0.001    B/op
StringFormat.stringIntFormat                                        avgt   25   576.423 ±   4.596   ns/op
StringFormat.stringIntFormat:·gc.alloc.rate.norm                    avgt   25   432.034 ±   0.002    B/op
StringFormat.widthStringFormat                                      avgt   25   999.835 ±  20.127   ns/op
StringFormat.widthStringFormat:·gc.alloc.rate.norm                  avgt   25   525.509 ±  14.742    B/op
StringFormat.widthStringIntFormat                                   avgt   25  1332.163 ±  30.901   ns/op
StringFormat.widthStringIntFormat:·gc.alloc.rate.norm               avgt   25   720.715 ±   8.798    B/op


Patch:

Benchmark                                                           Mode  Cnt     Score    Error   Units
StringFormat.complexFormat                                          avgt   25  8840.089 ± 51.222   ns/op
StringFormat.complexFormat:·gc.alloc.rate.norm                      avgt   25  1736.151 ±  0.009    B/op
StringFormat.stringFormat                                           avgt   25   247.310 ±  2.091   ns/op
StringFormat.stringFormat:·gc.alloc.rate.norm                       avgt   25   248.018 ±  0.001    B/op
StringFormat.stringIntFormat                                        avgt   25   565.487 ±  6.572   ns/op
StringFormat.stringIntFormat:·gc.alloc.rate.norm                    avgt   25   408.032 ±  0.002    B
StringFormat.widthStringFormat                                      avgt   25   970.015 ± 32.915   ns/op
StringFormat.widthStringFormat:·gc.alloc.rate.norm                  avgt   25   449.991 ± 25.716    B/op
StringFormat.widthStringIntFormat                                   avgt   25  1284.572 ± 28.829   ns/op
StringFormat.widthStringIntFormat:·gc.alloc.rate.norm               avgt   25   636.872 ±  7.331    B/op

-------------

Commit messages:
 - Fix call with null Formatter
 - 8278642: Refactor Formatter

Changes: https://git.openjdk.java.net/jdk/pull/6821/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6821&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278642
  Stats: 333 lines in 1 file changed: 0 ins; 39 del; 294 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6821.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6821/head:pull/6821

PR: https://git.openjdk.java.net/jdk/pull/6821