[GTK] Replacing usages of Display#getDPI from gtk

[ShahzaibIbrahim]

This is a preparatory commit to remove all possible usages of getDPI from gtk. Since getDPI is set to be deprecated.

PR for Deprecation: #2872

[github-actions]

Test Results (linux)

   88 files     88 suites   14m 24s ⏱️
4 557 tests 4 337 ✅ 220 💤 0 ❌
  211 runs    208 ✅   3 💤 0 ❌

Results for commit 49536d1.

♻️ This comment has been updated with latest results.

[jonahgraham]

The GTK3 tests hung after 360m - I don't think that is because of your change and I have raised #2876 to track that

[HeikoKlare]

Having the scale factor being based on the screen DPI leads to unexpected result e.g. Image too big/small. Having a screen dpi independent factor leads to consistent results.

I do not understand how the commit/PR message relates to the actual change. What unexpected results to you refer to? Can you share an example?

And can you explain why it is correct to use a fixed DPI value of 96 in Display, even though the current getDPI() implementation has more sophisticated logic to determine the actual DPI? Should the implementation of getDPI() be changed then, in case the value is wrong?

[ShahzaibIbrahim]

Having the scale factor being based on the screen DPI leads to unexpected result e.g. Image too big/small. Having a screen dpi independent factor leads to consistent results.

I do not understand how the commit/PR message relates to the actual change. What unexpected results to you refer to? Can you share an example?

And can you explain why it is correct to use a fixed DPI value of 96 in Display, even though the current getDPI() implementation has more sophisticated logic to determine the actual DPI? Should the implementation of getDPI() be changed then, in case the value is wrong?

After our discussion. I have changed the commit message and its content. Now we only get rid of getDPI usage only where its possible. For Display getDPI could be used for both Device and Printer both and because of this some places the value currently cannot be replaced.

For later: we can deprecate the getDPI method now, but later we can keep the usage to internal by making getDPI package protected.

[HeikoKlare]

Reusing the already stored DPI value instead of re-retrieving it is fine to avoid unnecessary multiple calls to getDPI().