Add type for Hex color

[ximex]

add a type for hex-color strings that is a bit stricter than only string.
type HexColor = `#${string}`;

[jaywcjlove]

@ximex I can add this type to the package. I tried using the HexColor type, but it may not be easy to use in the code because many places have done error handling, which causes type errors.

react-color/packages/color-convert/src/index.ts

Lines 335 to 336 in 632d4e9

	// To compare colors like `#FFF` and `ffffff` we convert them into RGB objects
	return equalColorObjects(hexToRgba(first), hexToRgba(second));

react-color/packages/color-convert/src/index.ts

Line 339 in 632d4e9

export const validHex = (hex: string): boolean => /^#?([A-Fa-f0-9]{3,4}){1,2}$/.test(hex);

[ximex]

is already done here: https://github.com/uiwjs/react-color/pull/155/files#diff-4a1d4aef5f7a97716359b980c22ef670d78d5f779651e57fe94589767051e95bR306