RFR: 8262744: Formatter '%g' conversion uses wrong format for BigDecimal rounding up to limits

[Ian Graves]

This fixes a bug where the formatting code for `%g` flags incorrectly tries to round `BigDecimal` after determining whether it should be a decimal numeric format or a scientific numeric format. The solution rounds before determining the correct format.

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Commit messages:
 - Fixing rounding issue with BigDecimal and %g formatting flags

Changes: https://git.openjdk.java.net/jdk/pull/3363/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3363&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262744
  Stats: 59 lines in 2 files changed: 59 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3363.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3363/head:pull/3363

PR: https://git.openjdk.java.net/jdk/pull/3363