Custom extension of DocJavaMethod.

[younker99]

Summary(关于这个pr的描述)

Before converting List to List, invoke custom extensions for adjustments.
在List<DocJavaMethod>转化为List<ApiMethodDoc>前，调用自定义的拓展进行调整。`

Basic example(pr的用例)

Preliminary design is as follows:

1. Define ICusJavaMethodExtension with the content being List<DocJavaMethod> apply(JavaClass cls, List<DocJavaMethod> methodList).
2. Add an ICusJavaMethodExtension cusJavaMethodExtension attribute to ApiConfig.
3. In IRestDocTemplate, before converting List<DocJavaMethod> to List<ApiMethodDoc> within the buildEntryPointMethod, check and invoke cusJavaMethodExtension to update the List<DocJavaMethod>.

初步设计是

1. 定义ICusJavaMethodExtension,内容为List<DocJavaMethod> apply(JavaClass cls, List<DocJavaMethod> methodList)
2. ApiConfig中添加ICusJavaMethodExtension cusJavaMethodExtension属性
3. 在IRestDocTemplate中buildEntryPointMethod里，List<DocJavaMethod>转化为List<ApiMethodDoc>前，判断并调用cusJavaMethodExtension，更新List<DocJavaMethod>

Motivation(提出这个pr目的)

The common controller encapsulated in the project features multiple levels of inheritance, with some methods having dynamic return types and parameters. The type information parsed by smart-doc for these interfaces is inaccurate and cannot be adjusted.

项目中封装的通用controller存在多层继承，部分method的返回值和入参是动态类型，此部分接口smart-doc解析出的类型信息不准确，却又无法调整。

[shalousun]

@younker99 You can supplement the examples in the test project at https://github.com/smart-doc-group/smart-doc-example-cn first. Wouldn't it be better to rename ICusJavaMethodExtension to ICustomJavaMethodHandler, as smart-doc does not advocate for using non-generic terms that are too specific? Start by adding examples and then submit a PR.

[younker99]

@shalousun
smart-doc-group/smart-doc-example-cn#20
Controller sample has been supplemented.

[shalousun]

@shalousun smart-doc-group/smart-doc-example-cn#20 Controller sample has been supplemented.

merged