* refactor: migrate database/users_spec.js to ts
- migrate file autocomplete/database/users_spec.js to typescripts
- udpate system.d.ts data type adding type
for shouldHaveElasticsearchDisabled
* refactor: migrate users_in_channel_switcher_spec.js
- migrate file users_in_channel_switcher_spec to typescript
- fix issue with data type on file autocomplete/helpers.ts
function verifySuggestionAtChannelSwitcher
- fix issue with data type on file autocomplete/common_test.ts
function doTestQuickChannelSwitcher
* refactor: migrate users_in_message_input_box_spec to ts
- migrate file database/users_in_message_input_box_spec.js to typescript
- migrate file support/ui/suggestion_list.js to typescript and update
docs and type definitions
- update references to doTestPostextbox function
- update references to verifySuggestionAtPostTextbox function
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