Re-enable checkstyle

[manastalukdar]

At this point CheckStyle seems to provide style guidelines that conflict with Google formatting settings.

Formatting setting:

"java.format.settings.url": "https://raw.githubusercontent.com/google/styleguide/gh-pages/eclipse-java-google-style.xml",
"java.format.settings.profile": "GoogleStyle",

CheckStyle setting:

"java.checkstyle.configuration": "https://raw.githubusercontent.com/checkstyle/checkstyle/master/src/main/resources/google_checks.xml"

Related issue:

• Track vscode-checkstyle issue with java.checkstyle.configuration pointing to url for google checks #56

Also relevant:

CheckStyle has some breaking changes from 8.18 to 8.23.

The workaround is to change the URL to: https://raw.githubusercontent.com/checkstyle/checkstyle/checkstyle-8.18/src/main/resources/google_checks.xml