RFR: 8267551: Support loading images from inline data-URIs [v6]

[Michael Strauß]

> This PR adds support for loading images from [inline data URIs](https://en.wikipedia.org/wiki/Data_URI_scheme), which is also widely supported by web browsers. This enables developers to package small images in CSS files, rather than separately deploying the images alongside the CSS file.

Michael Strauß has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Merge branch 'master' into feature/image-datauri
 - Moved test
 - Added javadoc
 - Added javadoc
 - Added javadoc
 - Added javadoc
 - Added data-URI loading support for images

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/508/files
  - new: https://git.openjdk.java.net/jfx/pull/508/files/3a77ac0b..4302e9f1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=508&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=508&range=04-05

  Stats: 683 lines in 52 files changed: 400 ins; 98 del; 185 mod
  Patch: https://git.openjdk.java.net/jfx/pull/508.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/508/head:pull/508

PR: https://git.openjdk.java.net/jfx/pull/508