fix(dropdown): improve accessibility keyboard navigation of dropdown

Prior behavior: tabbing would focus the dropdown and open it, subsequent tabs would focus on each
item of the list. Instead, the desired behavior is one tab opens the list, only the up and down keys
can be used to navigate the list, then the next tab would close list. For this refactor I set the
tabIndex to -1 to disable focus on the list items. I also removed the tabIndex from the Container
and adjusted the keyHandler toassign focus from the button instead of the container. This was
because there was always an extra tab needed to close and leave the dropdown because both the
container and button were being traveresed. Since the butten needs the focus--disabling wasn't an
option.

#210

src/components/Dropdown/Dropdown.tsx

@@ -375,8 +375,8 @@ const Dropdown = ({
             }
             break;
           case 'ArrowDown':
-            if (focusedElement && focusedElement.id === `${name}-container`) {
-              const optionsContainer = focusedElement.children[1];
+            if (focusedElement && focusedElement.id === `${name}-button-value`) {
+              const optionsContainer = focusedElement.nextElementSibling;
               if (optionsContainer) {
                 const toFocus = optionsContainer.children[0] as HTMLElement | undefined;
                 if (toFocus) {
@@ -447,7 +447,6 @@ const Dropdown = ({
         setIsOpen(true);
       }}
       ref={mergeRefs([containerRef, containerInternalRef])}
-      tabIndex={tabIndex}
       {...containerProps}
     >
       <Button
@@ -522,7 +521,7 @@ const Dropdown = ({
               key={`${name}-option-${option.id}`}
               onBlur={handleBlur}
               onClick={() => handleSelect(option.id)}
-              tabIndex={tabIndex}
+              tabIndex={-1}
               color={defaultedColor}
               variant={optionsVariant}
               multi={multi}