ColorChannelSelector: add tooltip, fix toggle_button repositioning and channels autotranslation

[arkology]

Changes:

• Fixed issue with toggle_button changing its position, caused by the panel size.
• Added tooltip for toggle_button to clarify its purpose.
• Prevented accidental translation of color channel names in certain languages (e.g., Arabic).
• Updated toggle_button theming to use "PreviewLightButton" type variation, aligning it with similar buttons (like in MaterialEditor).
• Code cleanup: EditorScale::get_scale() replaced with more common EDSCALE, removed CHANNEL_COUNT (it was inconsistentty used anyway), removed debug error checks from create_button() (redundant, the function is only called in constructor and with known arguments) use CHANNEL_COUNT everywhere (see ColorChannelSelector: add tooltip, fix toggle_button repositioning and channels autotranslation #104474 (comment)).

4.5dev1:

NVIDIA_Share_WlYS839r7b.mp4

This PR:

godot.windows.editor.dev.x86_64_cghwXM6u7K.mp4

[arkology]

I suppose this one still may fit 4.5 because it fixes several bugs in ColorChannelSelector. If some changes are unnecessary (code cleanup, theme tweaks) I can just drop them.
@KoBeWi could you please take a look? Thanks.

[KoBeWi]

I'm not sure about removing the constant. If it was not used consistently, then you can make it consistent.

Other changes are fine.

[arkology]

Got it, thanks. I'll revert all code style changes I made in PR (even if code style is inconsistent, it doesn't affect functionality).

[arkology]

Pushed commit without codestyle changes. The only "codestyle" changes are:

• CHANNEL_COUNT is used everywhere (according to ColorChannelSelector: add tooltip, fix toggle_button repositioning and channels autotranslation #104474 (review))
• EDSCALE is used instead of EditorScale::get_scale() (according to Add color channel filter to editor texture previews #100157 (comment))

[AThousandShips]

Can't speak to the code but approving on style

[Repiteo]

Thanks!