RFR: 8176501: Method Shape.getBounds2D() incorrectly includes Bezier control points in bounding box [v5]

[Jeremy]

> This removes code that relied on consulting the Bezier control points to calculate the Rectangle2D bounding box. Instead it's pretty straight-forward to convert the Bezier control points into the x & y parametric equations. At their most complex these equations are cubic polynomials, so calculating their extrema is just a matter of applying the quadratic formula to calculate their extrema. (Or in path segments that are quadratic/linear/constant: we do even less work.)
> 
> The bug writeup indicated they wanted Path2D#getBounds2D() to be more accurate/concise. They didn't explicitly say they wanted CubicCurve2D and QuadCurve2D to become more accurate too. But a preexisting unit test failed when Path2D#getBounds2D() was updated and those other classes weren't. At this point I considered either:
> A. Updating CubicCurve2D and QuadCurve2D to use the new more accurate getBounds2D() or
> B. Updating the unit test to forgive the discrepancy.
> 
> I chose A. Which might technically be seen as scope creep, but it feels like a more holistic/better approach.
> 
> Other shapes in java.awt.geom should not require updating, because they already identify concise bounds.
> 
> This also includes a new unit test (in Path2D/UnitTest.java) that fails without the changes in this commit.

Jeremy has updated the pull request incrementally with one additional commit since the last revision:

  8176501: Method Shape.getBounds2D() incorrectly includes Bezier control points in bounding box
  
  Addressing code review recommendation to calculate polynomial coefficients using differences / vector notation.
  
  https://github.com/openjdk/jdk/pull/6227#discussion_r743534560
  
  I generally understand the intention of this change, but I don't know exactly how to test/evaluate it.
  
  The unit tests still pass. I ran some sample calculations involving a 100x100 Ellipse2D as it was rotated, and the two getBounds2D(..) implementations (before and after this commit) only differed by a few ulps (usually around 10^-15), as expected.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6227/files
  - new: https://git.openjdk.java.net/jdk/pull/6227/files/e617c722..b7ca69c8

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6227&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6227&range=03-04

  Stats: 19 lines in 1 file changed: 10 ins; 0 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6227.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6227/head:pull/6227

PR: https://git.openjdk.java.net/jdk/pull/6227