Build-time flag to exclude Icu4j

[aeriksson]

When compiling JVM polyglot projects that include GraalJS using native-image, a somewhat large chunk (~8MB) of the resulting binary comes from Icu4j.

This mostly consists of locale-specific data, and is mostly/exclusively used for the JS Intl. API. Since support for this API can be disabled, it'd be great if there was a corresponding flag to exclude Icu4j from the build.