Feat: Corner Radii, Corner Shapes, and Custom UIBox Shapes

[Aikoyori]

This PR changes how corners are calculated. You can now specify how each corner's radius and corner jaggedness

some absurd example here

G.FUNCS.overlay_menu({
    definition = create_UIBox_generic_options({
        back_func = "settings",
        contents = {
                { n = G.UIT.R, config = { colour = G.C.RED, r = 1, res = {5}, corners = {{0,0.1,0.2,0.4,0.8,1.6,3.2,4},{0,0.1,0.2,0.4,0.8,1.6,3.2,4},{0,0.1,0.2,0.4,0.8,1.6,3.2,4},{0,0.1,0.2,0.4,0.8,1.6,3.2,4}}, minw = 10, minh = 5 }}
            }
        })
    }) 

Additional Info:

• I didn't modify api's or I've made a PR to the wiki repo.
• I didn't modify api's or I've updated lsp definitions.
• I didn't make new lovely files or all new lovely files have appropriate priority.

[Aikoyori]

I have added an ability to completely customize the shape of UIBoxes'