fix(FocusTrapZone): firstFocusableSelector is fragile

[sophieH29]

Fixes #1566

Breaking change

Before:
firstFocusableSelector was used only to specify the class name string selector. . was appended to the passed value.

After:
firstFocusableSelector can be any string selector as is used in API for document.querySelector

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This PR introduces changes to FocusTrapZone and AutoFocusZone to not limit a user to using class selectors only.
Now it's a user responsibility to pass the whole string selector whether it's a .blah or #blah or tag blah etc. If this element won't be found in the container, the first tabbable element will be selected

[codecov]

Codecov Report

Merging #1732 into master will not change coverage.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master    #1732   +/-   ##
=======================================
  Coverage   70.98%   70.98%           
=======================================
  Files         860      860           
  Lines        7156     7156           
  Branches     2058     2078   +20     
=======================================
  Hits         5080     5080           
  Misses       2070     2070           
  Partials        6        6

Impacted Files	Coverage Δ
.../src/lib/accessibility/FocusZone/FocusTrapZone.tsx	70.58% <0%> (ø)	⬆️
.../src/lib/accessibility/FocusZone/AutoFocusZone.tsx	100% <100%> (ø)	⬆️

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[layershifter]

Please describe breaking changes in PR description 😼