perf(statuscolumn): only fill click defs array once per redraw (#21884)

Problem:    'statuscolumn' click definitions are cleared, evaluated,
            allocated and filled each redraw for every row in a window.
            This despite the fact that we only store a single click
            definition array for the entire column as opposed to one
            for each row.
Solution:   Only fill the 'statuscolumn' click definition array once per
            window per redraw.

Resolve https://github.com/neovim/neovim/issues/21767.

test/functional/ui/statuscolumn_spec.lua

@@ -61,7 +61,7 @@ describe('statuscolumn', function()
     ]])
   end)
 
-  it("works with 'statuscolumn'", function()
+  it("works with 'number' and 'relativenumber'", function()
     command([[set stc=%{&nu?v:lnum:''}%=%{&rnu?'\ '.v:relnum:''}│]])
     screen:expect([[
       4 │aaaaa                                             |