RFR: 8264999: GeneralPath.lineTo() to itself produces jagged lines [v2]

[Jeremy]

> Previously when you drew a line that moved exactly (+0, +0) with a miter stroke the Stroker class acted like a horizontal miter was appropriate. Now we abort instead, so no miter is applied.
> 
> The new unit test tests the original steps plus several variations.
> 
> I'm a little nervous about this change because it looks like someone previously considered this exact condition and implemented a different behavior. I don't think I understand the original rationale.

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

  JDK-8264999: GeneralPath.lineTo() to itself produces jagged lines
  
  Adding "&& prev == DRAWING_OP_TO" per Laurent's code review.
  
  I also redid the unit tests. Before this change, with the new unit tests: one scenario failed. With this change: four scenarios failed.
  
  For now I've commented out the failing tests. The failing tests are not the same as the original bug; they are related considerations we should also test against, but IMO they are not essential for the resolution of jdk-8264999.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8943/files
  - new: https://git.openjdk.java.net/jdk/pull/8943/files/7c29da9d..c7e35275

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8943&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8943&range=00-01

  Stats: 248 lines in 2 files changed: 124 ins; 26 del; 98 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8943.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8943/head:pull/8943

PR: https://git.openjdk.java.net/jdk/pull/8943