allowing to use context from any type of SPFx extensions

[AJIXuMuK]

Q	A
Bug fix?	[ ]
New feature?	[x]
New sample?	[ ]
Related issues?	mentioned in #408

What's in this Pull Request?

Code changes to allow controls to be used in any type of SPFx components: web parts or extensions

[codecov-io]

Codecov Report

Merging #419 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #419   +/-   ##
=======================================
  Coverage   73.31%   73.31%           
=======================================
  Files          18       18           
  Lines         802      802           
  Branches      164      154   -10     
=======================================
  Hits          588      588           
  Misses        164      164           
  Partials       50       50

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