The update by query action parses a script from an object (map or string). We will need to do the same for runtime fields as they are parsed as part of mappings (#59391).
This commit moves the existing parsing of a script from an object from RestUpdateByQueryAction to the Script class. It also adds tests and adjusts some error messages that are incorrect. Also, options were not parsed before and they are now. And unsupported fields trigger now a deprecation warning.
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