RFR: JDK-8283124: Add constant for tau to Math and StrictMath

[Brian Burkhalter]

On Mon, 14 Mar 2022 20:52:39 GMT, Joe Darcy <darcy at openjdk.org> wrote:

> Add a constant for tau, 2*pi, to Math and StrictMath. Since 2*pi is a very common value in mathematical formulas, it is helpful to give it a distinct constant.
> 
> Please also review the CSR https://bugs.openjdk.java.net/browse/JDK-8283136

Marked as reviewed by bpb (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/7813