encoding/form: support repeated filed map from path etc.

[Cluas]

Description (what this PR does / why we need it):

#1193

Other special notes for reviewer:

Now there is no compulsion to use the same legal separator, which means that the user can use the format a b,c|d\te, which will also be legally parsed as []string{"a", "b", "c", "d", "e"}, I'm not sure if this is good practice, maybe we can restrict it to a single legal separator.

[codecov-commenter]

Codecov Report

Merging #1512 (da0625e) into main (7cc6565) will increase coverage by 0.23%.
The diff coverage is 83.87%.

@@            Coverage Diff             @@
##             main    #1512      +/-   ##
==========================================
+ Coverage   68.56%   68.80%   +0.23%     
==========================================
  Files          67       67              
  Lines        3089     3119      +30     
==========================================
+ Hits         2118     2146      +28     
  Misses        791      791              
- Partials      180      182       +2     

Impacted Files	Coverage Δ
encoding/form/form.go	67.56% <0.00%> (ø)
encoding/form/proto_decode.go	27.11% <86.66%> (+9.16%)	⬆️
transport/http/binding/bind.go	33.33% <0.00%> (+33.33%)	⬆️

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[Cluas]

Considering the complexity, it is recommended to first pass the array via parameter instead of path, something like id=1&id=2, to temporarily turn off this PR.