fix(core): indexes need exclude incomplete number

[frehaiku]

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What have you changed?

修复 path 为 array.0.a2 时，index 属性取值为 NaN 的问题
https://codesandbox.io/s/mystifying-curran-s137rx?file=/src/App.vue

[codecov]

Codecov Report

Base: 96.17% // Head: 96.17% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (74a42cb) compared to base (b3d3eb7).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@              Coverage Diff              @@
##           formily_next    #3437   +/-   ##
=============================================
  Coverage         96.17%   96.17%           
=============================================
  Files               152      152           
  Lines              6590     6593    +3     
  Branches           1840     1777   -63     
=============================================
+ Hits               6338     6341    +3     
- Misses              223      252   +29     
+ Partials             29        0   -29     

Impacted Files	Coverage Δ
packages/core/src/models/BaseField.ts	100.00% <100.00%> (ø)
packages/antd/src/__builtins__/moment.ts	96.42% <0.00%> (-0.64%)	⬇️
packages/next/src/__builtins__/moment.ts	96.66% <0.00%> (-0.56%)	⬇️
packages/path/src/index.ts	65.25% <0.00%> (ø)
packages/path/src/parser.ts	92.42% <0.00%> (ø)
packages/path/src/shared.ts	50.87% <0.00%> (ø)
packages/vue/src/shared/h.ts	86.48% <0.00%> (ø)
packages/reactive/src/tree.ts	100.00% <0.00%> (ø)
packages/path/src/tokenizer.ts	91.74% <0.00%> (ø)
packages/reactive/src/array.ts	100.00% <0.00%> (ø)
... and 10 more

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