[css-images-4] Relax color interpolation method syntax in gradients

[cdoublev]

Please forgive me if some related discussions exist somewhere but I did not find them in #6667 or #5833. I would like to know why the color interpolation method cannot be declared between the gradient line parameters (I am not sure this is the correct term).

For example:

• current: conic-gradient([[from <angle>]? [at <position>]?] || <color-interpolation-method>, <angular-color-stop-list>)
• instead of conic-gradient([from <angle> || at <position> || <color-interpolation-method>]?, <angular-color-stop-list>)

From the perspective of the authoring experience, conic-gradient(at center in srgb from 45deg, ...) does not seem even more meaningless (no criticism here) than conic-gradient(at center in srgb, ...) for me, and the syntax is easier to read.

[cdoublev]

Also, I think that all gradient syntaxes are incorrect because they all require one or more (||) of:

• the gradient line parameters
• the color interpolation method followed by comma followed by the color stop list

conic-gradient([[from <angle>]? [at <position>]?] || <color-interpolation-method>, <angular-color-stop-list>)
linear-gradient([<angle> | to <side-or-corner>]? || <color-interpolation-method>, <color-stop-list>)
radial-gradient([[<ending-shape> || <size>]? [at <position>]?] || <color-interpolation-method>, <color-stop-list>)

I think that the intent is:

conic-gradient([[from <angle>]? [at <position>]? || <color-interpolation-method>]?, <angular-color-stop-list>)
linear-gradient([[<angle> | to <side-or-corner>] || <color-interpolation-method>]?, <color-stop-list>)
radial-gradient([[<ending-shape> || <size>]? [at <position>]? || <color-interpolation-method>]?, <color-stop-list>)

Obviously, the color stop list is mandatory.