Feature runtime.Validateable for for parameters

[mwieser]

Regarding #2309. Add a Validate method to the parameter generation, which reuses the validate methods of the properties if present. Refactored the parameter.gotml to have reusable code for binding and validation code generation. Added the GenParameterValidateOnly and GenItemsValidateOnly structs for this to pass a GenParameter/GenItems to a template to only generate the code necessary for validation.

This removes reassigning array/slice properties in the validation methods. As mentioned in #2309, it seems that the reassignment of the property is not necessary in the validation methods and I therefore removed it to remove side effects from the validation methods. In case the binding in the validate methods is needed, the step would need to be added again.

The reason for this PR is to validate parameter structs without having to bind them. This can be helpful when validating the params on a client before sending them. Furthermore the method exists for models so it would be more unified.

[codecov]

Codecov Report

Attention: 32 lines in your changes are missing coverage. Please review.

Comparison is base (5759dce) 82.13% compared to head (53b4f64) 82.30%.
Report is 397 commits behind head on master.

Files	Patch %	Lines
generator/types.go	81.81%	25 Missing and 1 partial ⚠️
cmd/swagger/commands/serve.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2387      +/-   ##
==========================================
+ Coverage   82.13%   82.30%   +0.17%     
==========================================
  Files          50       50              
  Lines        8563     8681     +118     
==========================================
+ Hits         7033     7145     +112     
- Misses       1032     1043      +11     
+ Partials      498      493       -5     

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[casualjim]

Hi,

I'm sorry I missed this PR. Would it be possible to bring it up to date so I can merge it?