RFR: 8329098: Support "@1x" image naming convention as fallback [v4]

[Lukasz Kostyra]

> This PR adds a title-mentioned fallback to `ImageStorage.java` and a test for that specific scenario.
> 
> In `ImageStorage.loadAll()` we still prefer the Image path that was provided by the user, but if it is missing we will now try to add a `@1x` suffix to Image name and give it one last try.
> 
> Added test includes a binary file `checkers at 1x.png`. This was added to differentiate it from the collection of `checker.png` files and their higher scale variants, but it is a direct copy of already existing `checker.png` test resource, just with a different name and suffix. Test should fail without a change in `ImageStorage.java` and pass with it.

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

  Store and rethrow exception from main createInputStream()

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1598/files
  - new: https://git.openjdk.org/jfx/pull/1598/files/96155157..932eed38

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1598&range=03
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1598&range=02-03

  Stats: 8 lines in 1 file changed: 3 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1598.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1598/head:pull/1598

PR: https://git.openjdk.org/jfx/pull/1598