Before, auto-completion was based on on-air resolve, and
'FirTowerDataContext' was computed once, during creation of the
dependent analysis session (with using 'FirTowerDataContextCollector').
This allowed to return the context almost instantly, no matter how many
completion candidates there were.
Dangling file resolution doesn't use 'FirTowerDataContextCollector', as
now there is more precise 'ContextCollector'. However,
'ContextCollector' doesn't cache results by itself, and, if asked, it
will compute the same context over and over again. This exact happened
with extension applicability checker.
The optimized implementation maintains a checker object which caches the
computed context. The old end-point is left to give the IDE plugin time
to adapt to the change.
^KTIJ-28445
Yan Zhulanow
57dcd645b1