Create new shared filter component

The rigidity of the current simple_filter.vue makes it very difficult to extend or even be applicable to all the filter dropdowns (often we need to override the base functions). In this issue, let's create a new shared component that captures the common functionalities of the filter dropdown and let the individual filter dropdown take care of their own customization.

Implementation thoughts:

• Ideally, we should use the composition API to create this shared component. However, the migration to Vue 2.7 is still a WIP > #375595 (closed)
• As an iterative approach, we can explore the use of mixins (and create a follow up to convert it to the composition API at a later date).

Verification steps

• Verify that querystring_sync.vue exists.
• Verify that querystring_sync_spec.js exists.
• Verify that dropdown_button_text.vue exists.
• Verify that dropdown_button_text_spec.js exists.