Image Editor: Add support for importing palette files made by external art tools

Is your feature request related to a problem?

The current sprite editor is powerful enough that, even if the original art was made in some other tool (like photoshop or aseprite), it is usually more comfortable to make all changes, even major ones, within Gamemaker.

That said, once I open any sprite, the first step is always using the eyedropper on every color so that it fills the color history with my palette. A palette I already created and had access to in my previous tool.

Describe the solution you'd like

.PAL files are very simple and standardized palette files that could easily be imported into GameMaker in the existing "Colours" section of the image editor.

Describe alternatives you've considered

Sometimes, especially when I am trying to hold a very strict color palette, I go through the trouble of Ctrl+Clicking on every pallete swatch and copy/pasting the hex code from my other image editing tool. And every time by the time I finish I come to the conclusion that it would have been faster to reopen the image in my original software, make the changes, and re-import the files into GameMaker over a dozen times.

Additional context

No response

YoYoGames / GameMaker-Bugs