[BUG] inconsistent return types for `request:get-data`

[line-o]

Describe the bug

While request:get-data() returns xs:base64Binary for request bodies encoded as application/json it returns and instance of xs:string for application/json-patch+json.

Expected behavior

request:get-data() should return the same datatype for all requests with JSON encoded data in the body.

• application/json
• any application type with a subtype ending in +json

To Reproduce

TBD see https://github.com/eeditiones/roaster/pull/59

Context (please always complete the following information):

• OS: macOS 12.5.1
• eXist-db version: 6.1.0-SNAPSHOT 9e0bd5d367d3737443f9d2b378f3cac515a70c75
• Java Version Java8u342

Additional context

• How is eXist-db installed? built from source
• Any custom changes in e.g. conf.xml? none