Simplified Store Publisher

[StevenLambion]

This PR removes what's left of the original action-based update implementation used during the beta period of SwiftUI. It also replaces the AnyPublisher type with a dedicated StorePublisher type. In testing, these changes provides a small boost in performance and reduce the overall complexity of the library.

Work Performed

• Removed ActionType from the Store<_>'s didChange publisher.
• Updated StatePersistor so it no longer relies on the dispatched action.
• Removed StateBinder.
• Added a new StorePublisher type to replace AnyPublisher<, >.

[codecov-io]

Codecov Report

Merging #48 (9b69830) into 2.x (9ac73af) will increase coverage by 0.34%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              2.x      #48      +/-   ##
==========================================
+ Coverage   77.57%   77.92%   +0.34%     
==========================================
  Files          20       21       +1     
  Lines         446      453       +7     
==========================================
+ Hits          346      353       +7     
  Misses        100      100              

Impacted Files	Coverage Δ
Sources/SwiftDux/Store/StoreProxy.swift	70.00% <ø> (ø)
...wiftDuxExtras/Persistence/JSONStatePersistor.swift	72.72% <ø> (ø)
Sources/SwiftDux/State/OrderedState.swift	76.97% <100.00%> (+0.15%)	:arrow_up:
Sources/SwiftDux/Store/Store.swift	100.00% <100.00%> (ø)
Sources/SwiftDux/Store/StorePublisher.swift	100.00% <100.00%> (ø)
Sources/SwiftDux/Store/StoreReducer.swift	100.00% <100.00%> (ø)
...DuxExtras/Persistence/PersistStateMiddleware.swift	76.19% <100.00%> (ø)
...es/SwiftDuxExtras/Persistence/StatePersistor.swift	83.33% <100.00%> (-1.29%)	:arrow_down:

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