refactor: add a type property to router and state

[satya164]

The type property denotes the type of the router. It can be used to verify compatibility of navigation state and the router when rehydrating state, making rehydration more resilient.

It can also help our utilities to detect the type of the navigator to properly implement some functionality. For example, the useScrollToTop hook can now know if it's not inside a tab navigator and needs to find the tab navigator in a parent.

[codecov-io]

Codecov Report

Merging #146 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
+ Coverage    93.6%   93.65%   +0.05%     
==========================================
  Files          36       36              
  Lines         751      757       +6     
  Branches      197      199       +2     
==========================================
+ Hits          703      709       +6     
  Misses         39       39              
  Partials        9        9

Impacted Files	Coverage Δ
...ges/core/src/__tests__/__fixtures__/MockRouter.tsx	88.57% <ø> (ø)	⬆️
packages/routers/src/StackRouter.tsx	96.96% <ø> (ø)	⬆️
packages/routers/src/TabRouter.tsx	96.96% <ø> (ø)	⬆️
packages/core/src/useNavigationBuilder.tsx	98.76% <100%> (+0.06%)	⬆️
packages/routers/src/DrawerRouter.tsx	96.55% <100%> (ø)	⬆️
packages/core/src/useNavigationCache.tsx	96.29% <0%> (+0.29%)	⬆️

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