feat(dropdown): multiple selection

[bmdalex]

feat(dropdown): multiple selection

Description:

This PR implements the multiple selection with trigger button flavor for Dropdown component (easy to leverage existing functionality)

API

<Dropdown
  multiple
  items={inputItems}
  placeholder="Start typing a name"
  noResultsMessage="We couldn't find any matches."
/>

renders:

[codecov]

Codecov Report

Merging #845 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #845   +/-   ##
=======================================
  Coverage   93.54%   93.54%           
=======================================
  Files          21       21           
  Lines         728      728           
  Branches       69       73    +4     
=======================================
  Hits          681      681           
  Misses         47       47

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6a049c1...472c222. Read the comment docs.

[codecov]

Codecov Report

Merging #845 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #845   +/-   ##
=======================================
  Coverage   93.54%   93.54%           
=======================================
  Files          21       21           
  Lines         728      728           
  Branches       73       73           
=======================================
  Hits          681      681           
  Misses         47       47

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d89668f...d38f328. Read the comment docs.

[silviuaavram]

why do we need that parameter if we can get it from state as we did with the props? this method might as well be getTriggerButtonMessage or getTriggerButtonText. not important but was just curious why not like that. oh, and capital I in If there is no value...

[bmdalex]

this method is also used here, but not merged yet:
https://github.com/stardust-ui/react/pull/839/files#r254290634

with a different parameter, so the proposed name would not apply anymore, open to other naming suggestions

Will add capital "I", thanks