RFR: 8361286: Allow enabling of background loading for images loaded from an InputStream [v5]

[John Hendrikx]

> Support background loading of raw input streams
> 
> - Fixed generics (mix up of two ImageLoader types)
> - Removed unused code for handling headers, methods, request parameters
> - Use `long` for progress as streams may exceed 2 GB
> - Improved documentation of Image regarding background loading

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

  Clarify documentation with regards to stream closing

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1875/files
  - new: https://git.openjdk.org/jfx/pull/1875/files/65bc2507..6494c52a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1875&range=04
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1875&range=03-04

  Stats: 14 lines in 1 file changed: 6 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jfx/pull/1875.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1875/head:pull/1875

PR: https://git.openjdk.org/jfx/pull/1875