Timepicker is missing type declarations for the plugin

[stefanmo]

Describe the bug

When importing the FormTimepickerPlugin typescript throws an error that bootstrap-vue has no exported member FormTimepickerPlugin

Steps to reproduce the bug

1. Create a new vue project with typescript
2. Import FormTimepickerPlugin and use it in Vue.
3. Run project

Expected behavior

Typescript should not throw an error

Versions

Libraries:

• BootstrapVue: 2.9.0
• Bootstrap: 4.4.1
• Vue: 2.6.11
• typescript: 3.8.3

Environment:

• Device: PC
• OS: Linux

Demo link

Don't think it is necessary

Additional context

I can create a PR with the fix if desired.