feat(binding): use encoding.UnmarshalText by default via build tag

[takanuva15]

With this PR, users can set the build tag gin_bind_encoding to configure gin binding to use encoding.UnmarshalText by default. This will not break existing servers since the build tag must be specified to enable the behavior.

Credit to #4540 for the original default binding implementation

relates to #4540
relates to #4203
relates to #4177
relates to #3933
relates to #3045
relates to #3036
relates to #2673
relates to #2631
relates to #2510
closes #2423
closes #3060

Example

package main

import (
  "github.com/gin-gonic/gin"
  "github.com/gofrs/uuid"
)

func main() {
  route := gin.Default()
  var request struct {
    Uuid uuid.UUID `form:"uuid" binding:"uuid"`
  }

  route.GET("/test", func(ctx *gin.Context) {
    _ = ctx.BindQuery(&request)
    ctx.JSON(200, request)
  })
  _ = route.Run(":8088")
}

Test it with:

go run -tags=gin_bind_encoding main.go
# Then in another terminal
curl 'localhost:8088/test?uuid=70d9b500-fa26-11dd-876f-322495cdf0f7'

Result

{"Uuid":"70d9b500-fa26-11dd-876f-322495cdf0f7"}

Pull Request Checklist

Please ensure your pull request meets the following requirements:

• Open your pull request against the master branch.
• All tests pass in available continuous integration systems (e.g., GitHub Actions).
• Tests are added or modified as needed to cover code changes.
• If the pull request introduces a new feature, the feature is documented in the docs/doc.md.

Thank you for contributing!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.31%. Comparing base (3dc1cd6) to head (07bcf34).
⚠️ Report is 268 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4566      +/-   ##
==========================================
- Coverage   99.21%   98.31%   -0.90%     
==========================================
  Files          42       51       +9     
  Lines        3182     3152      -30     
==========================================
- Hits         3157     3099      -58     
- Misses         17       44      +27     
- Partials        8        9       +1     

Flag	Coverage Δ
	?
--ldflags="-checklinkname=0" -tags sonic	98.30% <100.00%> (?)
-tags gin_bind_encoding	98.30% <100.00%> (?)
-tags go_json	98.23% <100.00%> (?)
-tags nomsgpack	98.28% <100.00%> (?)
go-1.18	?
go-1.19	?
go-1.20	?
go-1.21	?
go-1.25	98.31% <100.00%> (?)
go-1.26	98.31% <100.00%> (?)
macos-latest	98.31% <100.00%> (-0.90%)	⬇️
ubuntu-latest	98.31% <100.00%> (-0.90%)	⬇️

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