Update to a Java 9+ Gradle wrapper

[pdigre]

World has moved away from Java 8 now, and Gradle 3.3 is also relatively old, version 6.0 has been around for a year !

[pdigre]

The JDK 8 from Oracle site is missing lib/tools.jar. The JDK8 from Red Hat on the other hand was complete. https://developers.redhat.com/products/openjdk/

[pdigre]

Another workaround:
run as admin - npm install --global windows-build-tools

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And now it wants to find a Visual Studio C++ version ???
You need to install the latest version of Visual Studio

gyp ERR! find VS including the "Desktop development with C++" workload.
gyp ERR! find VS For more information consult the documentation at:
gyp ERR! find VS https://github.com/nodejs/node-gyp#on-windows

[pdigre]

After the "gyp" fix I managed to compile, but there's something left out of the instructions.
It failed on src-gen directory whihc is missing.
Cannot find module 'C:\eclipse\git\theia-xtext\app\src-gen\backend\main.js'