Various features/fixes (#727)

* fix(data-table): export useStaticWidth prop

* docs(data-table): add static width example

* fix(data-table): do not render table header if title/description not provided

* feat(modal): dispatch "click:button--primary" as an alias to "submit"

* test: update DataTable types test

* test(modal): update modal type tests

* docs(data-table): add clear reminder to key headers/rows

src/ComposedModal/ComposedModal.svelte

@@ -53,6 +53,7 @@
     },
     submit: () => {
       dispatch("submit");
+      dispatch("click:button--primary");
     },
     declareRef: (ref) => {
       buttonRef = ref;