RFR: JDK-8329222: java.text.NumberFormat (and subclasses) spec updates

[Justin Lu]

Please review this PR which is a large spec reformatting for _java.text.NumberFormat_ and related subclasses, specifically DecimalFormat and CompactNumberFormat.

The motivation for this change was the difficulty of readability for these classes. This PR consists of changes such as better separating the text into sections with headers, advising to skip the pattern related sections if not needed, and general wording improvements.

To help with reviewing I have attached a [specdiff](https://cr.openjdk.org/~jlu/JDK-8329222/java.base/java/text/package-summary.html) as well as the built docs: [nFmt](https://cr.openjdk.org/~jlu/api/java.base/java/text/NumberFormat.html), [dFmt](https://cr.openjdk.org/~jlu/api/java.base/java/text/DecimalFormat.html), and [cnFmt](https://cr.openjdk.org/~jlu/api/java.base/java/text/CompactNumberFormat.html);

I will update the CSR once the wording is finalized.

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Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/18731/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18731&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329222
  Stats: 481 lines in 3 files changed: 166 ins; 152 del; 163 mod
  Patch: https://git.openjdk.org/jdk/pull/18731.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18731/head:pull/18731

PR: https://git.openjdk.org/jdk/pull/18731