Support reading pixel values from color 16 bit images (backport #699)

[mergify]

🎉 New feature

Closes #698

Summary

Add support for reading RGB[A] 16 bit images.

Similar to what's done in #439, this PR redirects the Pixel(...) function calls to use the PixelIndex(...) function which has been extended to support 16 bit color image formats.

Note: this PR does not entirely address the issue with the confusing flood of console messages about Image coordinates out of range.. when a format is not supported, see #698 (comment). The message is changed to a more generic one, i.e. Failed to to get pixel value at.. so it does not lead the user down the wrong path. We should still tackle this issue but we can do that in a separate PR.

Test it

Run the UNIT_Image_TEST

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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• Was GenAI used to generate this PR? If so, make sure to add "Generated-by" to your commits. (See this policy for more info.)

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---

This is an automatic backport of pull request #699 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 0e307e7 has failed:

On branch mergify/bp/gz-common5/pr-699
Your branch is ahead of 'origin/gz-common5' by 2 commits.
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You are currently cherry-picking commit 0e307e7.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   graphics/src/Image_TEST.cc

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   graphics/src/Image.cc

Cherry-pick of 3276a52 has failed:

On branch mergify/bp/gz-common5/pr-699
Your branch is ahead of 'origin/gz-common5' by 4 commits.
  (use "git push" to publish your local commits)

You are currently cherry-picking commit 3276a52.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   graphics/src/Image.cc

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[iche033]

resolved conflicts and force-pushed.

[codecov]

Codecov Report

❌ Patch coverage is 84.74576% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.55%. Comparing base (2d06bf7) to head (8173bd2).
⚠️ Report is 42 commits behind head on gz-common5.

Files with missing lines	Patch %	Lines
graphics/src/Image.cc	84.74%	9 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           gz-common5     #702      +/-   ##
==============================================
- Coverage       83.65%   80.55%   -3.10%     
==============================================
  Files              90       93       +3     
  Lines           10273    13702    +3429     
==============================================
+ Hits             8594    11038    +2444     
- Misses           1679     2664     +985     

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