Fix using uint suffix at the hex number declaration in shaders

[Chaosus]

Fix #78800 by allowing using 'u' suffix with the hex number:

[clayjohn]

Looks good. tested locally as well and it appears to work great

[akien-mga]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.1.

[AlfishSoftware]

This is a lexical change in *.gdshader(inc) grammar, right? I'll have to update it in my vscode extension grammar.
@Chaosus Does it allow only lowercase u or will 0xFFU be valid as well?

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Btw, I didn't find any mention of hex constants at all in https://docs.godotengine.org/en/stable/tutorials/shaders/shader_reference/shading_language.html#constants so when this is introduced, you might want to use the opportunity to add a little mention. E.g.:

Constants of the uint (unsigned int) type must have a u suffix to differentiate them from signed integers.
Alternatively, this can be done by using the uint(x) built-in conversion function.

uint a = 1u, b = uint(1);
uint c = 0xAu, d = uint(0xA);

[Chaosus]

Does it allow only lowercase u or will 0xFFU be valid as well?

Both, as well.