MultiSchemaField getting incorrect id when inside array

[QingqiShi]

Prerequisites

• I have read the documentation;
• In the case of a bug report, I understand that providing a SSCCE example is tremendously useful to the maintainers.
• Ideally, I'm providing a sample JSFiddle or a shared playground link demonstrating the issue.

Description

When MultiSchemaField is part of an array the idSchema is incorrectly generated. This can cause duplicated ids.

Steps to Reproduce

1. Check packages/core/test/anyOf_test.js
2. Find the test should correctly render form inputs for anyOf inside array items
3. Currently we're expecting input#root_foo to exist, but that's not the right id

Expected behavior

The idSchema ids should maintain the full id even if they're inside arrays.

For example, given a schema

const schema = {
  type: "object",
  properties: {
    items: {
      type: "array",
      items: {
        type: "object",
        anyOf: [
          {
            properties: {
              foo: {
                type: "string",
              },
            },
          },
          {
            properties: {
              bar: {
                type: "string",
              },
            },
          },
        ],
      },
    },
  },
};

The id for the foo field within each array item should be root_items_0_foo, root_items_1_foo etc.

Actual behavior

For the example above, the generated id is root_foo for all array items.

Version

2.4.1

[heath-freenome]

Fixed in v5 beta via #3039, see the 5.x migration guide