Allow arbitrary values with percentage in classes that support numbers and percentage values

[dcastil]

There are some classes which support numbers and percentages as arbitrary values in Tailwind CSS, e.g. brightness-[0.4] and brightness-[40%] are both equivalent. In tailwind-merge however, only numbers are supported in those. I should also add support for percentage values in those classes.

Affected theme groups:

• brightness
• contrast
• saturate
• scale

[dcastil]

Basically this: https://github.com/dcastil/tailwind-merge/blob/v1.14.0/src/lib/default-config.ts#L90

[dcastil]

Also the opacity theme group should only check for isArbitraryValue (e.g. by getNumberAndArbitrary()) since those classes are never ambiguous.