Add Java reachability rule and test file

What does this MR do and why?

Adds a Semgrep reachability rule to detect imports in Java code.

Important:

Some form of post-processing will likely be needed on the captured $LIB values, as the syntax makes it impossible to distinguish between package name and a symbol such as a class or constant, like:

import org.springframework.boot.SpringApplication;

In this scenario, the entire org.springframework.boot.SpringApplication will be captured in $LIB even though the dependency name is just org.springframework.boot. So post-processing is needed where parts between . are removed from right to left until the string matches a known dependency from the SBOM.

Related issues

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