feat(position): accept placement values with a space separated string

[fbasso]

No description provided.

[codecov-io]

Codecov Report

Merging #3034 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #3034   +/-   ##
=======================================
  Coverage   92.36%   92.36%           
=======================================
  Files          91       91           
  Lines        2909     2909           
  Branches      468      468           
=======================================
  Hits         2687     2687           
  Misses        163      163           
  Partials       59       59

Flag	Coverage Δ
#e2e	59.91% <100%> (ø)	⬆️
#unit	90.87% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
src/tooltip/tooltip.ts	98.46% <ø> (ø)	⬆️
src/typeahead/typeahead.ts	97.35% <ø> (ø)	⬆️
src/datepicker/datepicker-input.ts	97.1% <ø> (ø)	⬆️
src/popover/popover.ts	100% <ø> (ø)	⬆️
src/dropdown/dropdown.ts	98.31% <ø> (ø)	⬆️
src/util/positioning.ts	94.35% <100%> (ø)	⬆️

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[maxokorokov]

LGTM, thanks!

We need to properly test positionElements as there is a lot of "magic" happening there, especially with CSS classes adding/removing. But out of scope of this PR I guess.