(fix) use generic API selector instead of Android API

[leonjza]

Before this patch, using HotSpot would fail inside of Java.perform() with errors like:

TypeError: cannot convert to object
    at compileModule (node_modules/frida-java-bridge/lib/class-model.js:1324)
    at ensureInitialized (node_modules/frida-java-bridge/lib/class-model.js:1317)
    at build (node_modules/frida-java-bridge/lib/class-model.js:1227)
    at _make (node_modules/frida-java-bridge/lib/class-factory.js:287)
    at use (node_modules/frida-java-bridge/lib/class-factory.js:158)
    at enumerateMethods (node_modules/frida-java-bridge/index.js:312)
    at <anonymous> (agent/index.ts:9)
    at <anonymous> (node_modules/frida-java-bridge/lib/vm.js:35)
    at perform (node_modules/frida-java-bridge/index.js:370)
    at <anonymous> (agent/index.ts:9)

On a JVM target, android.getApi() returns null, so the first Java.* call that builds a class model fails tries to destruct jvmti from that null API object. This change switches class-model.js to import getApi() from lib/api.js instead of via lib/android.js, which is already the bridge's backend selector.

• On Android, lib/api.js continues to use android.getApi()
• On JVM, it falls back to jvm.getApi()

[leonjza]

Ah, saw too late, this is a dupe of #382 .