Replace deprecated Nashorn scripting implementation about imposter HOT 5 OPEN

GraalVM module added in 0288756.

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As of v1.3.0, the GraalVM implementation is now merged, but Nashorn is still the default.

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Currently Graal.js doesn't have special Map or List accessor syntax: oracle/graaljs#107

This makes accessing things like params more cumbersome:

Nashorn:

request.headers.Authorization
request.params.foo

Graal.js

request.headers.get('Authorization')
request.params.get('foo')

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Graal.js now supports map-like data structures as of v21.1.0

Added support for map-like data structures (issue #143) ... Java host interoperability was improved to handle java.util.Map implementations to make them look like guest language hash maps. This feature can be enabled and disabled with HostAccess.Builder.allowMapAccess(boolean).

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Bumped Graal version in 899487b to support the above.

Next step is enabling native compiler support to avoid using interpreted mode, per: https://www.graalvm.org/reference-manual/js/RunOnJDK/

This will likely require packaging changes and a possible move to JDK11 to reduce the number of build targets.

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