codemirror: use --primary-color for a cursor

[ildar170975]

All edit boxes in HA use --primary-color for a cursor:

But codemirror - not:

Suggest to use same --primary-color for a cursor in codemirror.

Currently it can be achieved by an external js file with

.cm-editor .cm-cursor { border-left-color: var(--primary-color) !important; }

Result is: