RFR: 8377427: Reduce substring allocations in Color.web(String, double) [v2]

[Michael Strauß]

> Color.web(string, double) parses a color string by creating substrings of the input. Almost all of these string allocations can be removed, except for an invocation of `Double.parseDouble(String)`, which doesn't have an overload that accepts a sub-range of the input string.
> 
> There are no new tests for this enhancement, since the existing tests already cover all relevant code paths.

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

  CSS-compliant double parser

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/2069/files
  - new: https://git.openjdk.org/jfx/pull/2069/files/95a305a2..040dc875

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=2069&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=2069&range=00-01

  Stats: 469 lines in 3 files changed: 468 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/2069.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2069/head:pull/2069

PR: https://git.openjdk.org/jfx/pull/2069