RFR: 8213045: Add commonly used symbolic math constants to the JDK

[Brian Burkhalter]

Add constant `java.math.BigDecimal.TWO`.

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Commit messages:
 - 8213045: Add commonly used symbolic math constants to the JDK

Changes: https://git.openjdk.java.net/jdk/pull/8735/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8735&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8213045
  Stats: 17 lines in 2 files changed: 12 ins; 2 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8735.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8735/head:pull/8735

PR: https://git.openjdk.java.net/jdk/pull/8735