improvement: allow assigning initialPossibleTypesMap for SSR use cases

[jackyef]

Hi, awesome library here! This library helped us to fetch instropection data on runtime to avoid loading them upfront on initial load.

We found that there is an issue when doing SSR. The SSR works and we can inject the serialised cache to the client side properly. But, upon hydrating, it seems like the client fails because it doesn't actually know about the possibleTypes information yet. We believe this is because the possibleTypes is still empty on the client side.

This PR adds a way to give an initialPossibleTypesMap to the fragment matcher.

[codecov-io]

Codecov Report

Merging #18 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #18   +/-   ##
=======================================
  Coverage   98.79%   98.79%           
=======================================
  Files           3        3           
  Lines          83       83           
  Branches       16       17    +1     
=======================================
  Hits           82       82           
  Misses          1        1           

Impacted Files	Coverage Δ
src/fragmentMatcher.js	97.82% <100.00%> (ø)

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