resolves #982

I've added an additional argument to each readValidatedBody, getValidatedQuery and getValidatedRouteParams which can be either an error object or a function that returns one. If a standard-schema is being used, then the issues array is available as an argument for the function variant.

This allows for the following custom error, which will ouput a markdown list of all the errors recorded:

import * as v from "valibot";

app.post("/", async (event) => {
  const body = await readValidatedBody(
    event,
    v.object({
      name: v.pipe(v.string(), v.minLength(3), v.maxLength(20)),
      age: v.pipe(v.number(), v.integer(), v.minValue(1)),
    }),
    (issues) => ({
      statusText: "Custom validation error",
      message: v.summarize(issues),
    }),
  );
});

I've also updated the defineValidatedHandler, which brings three more properties: bodyErrors, headersErrors and queryErrors. All allowing for either error object or function that returns one

Added two types, but I'm not super satisfied with ValidateIssues naming (I'm open for suggestions):

export type ValidateIssues = ReadonlyArray<Issue>;
export type ValidateError =
  | ErrorDetails
  | ((issues: ValidateIssues) => ErrorDetails);

I've also made sure that if a new HTTPError is thrown during validation, its content will be directly passed as is, quite useful for non-standard-schema validations.