Export the four advanced trainers, and write their hyperparameter rules into the schema

### Task Summary

The four advanced trainers implement `StandaloneCodeGenerator`. Each reads its hyperparameters from a table the user fills in rather than from fields of its own, so the script has to resolve, for every row, which parameter was chosen and what converter its value passes through before it reaches the estimator.

`JsonSchemaCustomizer` and its caller in `OperatorMetadataGenerator` come along because these four implement it. The rules a hyperparameter's value follows, the set it may take and the bound it must respect, are written into the schema at generation time, and without the call the schema carries none of them.

The KNN, SVC and SVR parameter tables gain the accepted values and the bounds each parameter actually admits, read from scikit-learn's own constraints rather than from recall.

Step 18 of 27 in #8325. It needs #8327 for the trait. The label column offered as one of its own inputs is filed separately as #8010 and closes with this work; #7979, #7952 and #7936 are part-of, since each is only fixed once the panel half in the editor step lands too.