Merge branch 'multi-os-pipelines' into 'master'

.github/workflows/checks.yaml

.gitignore

.idea/codeStyles/Project.xml

.idea/codeStyles/codeStyleConfig.xml

buildSrc/build.gradle

buildSrc/src/main/java/org/briarproject/onionwrapper/OS.java

.../src/main/java/org/briarproject/onionwrapper/OsUtils.java

.../main/java/org/briarproject/onionwrapper/StringUtils.java

.../test/java/org/briarproject/onionwrapper/StringUtils.java

...rc/test/java/org/briarproject/onionwrapper/TestUtils.java

onionwrapper-java/build.gradle

...est/java/org/briarproject/onionwrapper/BootstrapTest.java

...ava/org/briarproject/onionwrapper/ResourcesLinuxTest.java

...a/org/briarproject/onionwrapper/ResourcesWindowsTest.java