fix: editing/adding global colors when blocks are present is slow

[bfintal]

Adjustments:

• When adding global colors, fallback colors will no longer be updated
• When using global colors, fallback colors will no longer be added

Here's what this adjustment looks like:

- color: var(--stk-global-color-1234, #ff00ff);
+ color: var(--stk-global-color-1234);

[github-actions]

🤖 Pull request artifacts

file	commit
pr3299-stackable-3299-merge.zip	564a38e

[github-actions]

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[andeng1106]

@bfintal Text Color name is no longer showing when selecting existing global text colors in the palette. It's showing the var() instead:

Screen.Recording.2024-08-21.at.3.mp4