chore(core): avoid using rxjs/operators

[josepot]

There are a few good reasons for this change:

• Better performance
• Total bundle-size (in case that the consumer is not using these 3 operators)
• if one day the Observable proposal makes it through, then @core won't even need rxjs as a peer-dependency 🤯 . Let me dream, ok? 😅

[codecov[bot]]

Codecov Report

Merging #135 into main will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #135   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           26        26           
  Lines          366       371    +5     
  Branches        39        42    +3     
=========================================
+ Hits           366       371    +5     

Impacted Files	Coverage Δ
packages/core/src/internal/react-enhancer.ts	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 75ba112...92d845b. Read the comment docs.