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

tests/ComposedModal.test.svelte

@@ -10,7 +10,7 @@
   let checked = false;
 </script>
 
-<ComposedModal open>
+<ComposedModal open on:close on:click:button--primary>
   <ModalHeader title="Confirm changes" />
   <ModalBody hasForm>
     <Checkbox labelText="I have reviewed the changes" bind:checked />
@@ -19,6 +19,8 @@
     primaryButtonText="Proceed"
     primaryButtonDisabled="{!checked}"
     secondaryButtons="{[{ text: 'Cancel' }, { text: 'Duplicate' }]}"
-    on:click:button--secondary="{({ detail }) => {}}"
+    on:click:button--secondary="{({ detail }) => {
+      console.log(detail);
+    }}"
   />
 </ComposedModal>