Update definition.map.xml

[LucScu]

fix isMultipleFiles option for fileUploader component

Description (*)

isMultipleFiles option settings doesn't work for fileUploader element in the form ui_component xml.
Even if you add true it is not read and it remains false as default.

Manual testing scenarios (*)

1. create a field with fileUploader element in a form ui component
2. add the true
3. visit the page and you could add multiple files

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• README.md files for modified modules are updated and included in the pull request if any README.md predefined sections require an update
• All automated tests passed successfully (all builds are green)

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[LucScu]

@magento run all tests

[LucScu]

@magento run all tests

[LucScu]

@ihor-sviziev could you approve this pr?