RFR: 8301226: Add clamp() methods to java.lang.Math and to StrictMath [v5]

[Tagir F. Valeev]

> clamp() methods added to Math and StrictMath
> 
> `int clamp(long, int, int)` is somewhat different, as it accepts a `long` value and safely clamps it to an `int` range. Other overloads work with a particular type (long, float and double). Using similar approach in other cases (e.g. `float clamp(double, float, float)`) may cause accidental precision loss even if the value is within range, so I decided to avoid this.
> 
> In all cases, `max >= min` precondition should met. For double and float we additionally order `-0.0 < 0.0`, similarly to what Math.max or Double.compare do. In double and float overloads I try to keep at most one arg-check comparison on common path, so the order of checks might look unusual.
> 
> For tests, I noticed that tests in java/lang/Math don't use any testing framework (even newer tests), so I somehow mimic the approach of neighbour tests.

Tagir F. Valeev has updated the pull request incrementally with two additional commits since the last revision:

 - Tests refactoring
 - More clarifying comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12428/files
  - new: https://git.openjdk.org/jdk/pull/12428/files/065018f4..b758b8db

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12428&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12428&range=03-04

  Stats: 220 lines in 2 files changed: 84 ins; 36 del; 100 mod
  Patch: https://git.openjdk.org/jdk/pull/12428.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12428/head:pull/12428

PR: https://git.openjdk.org/jdk/pull/12428