Unify indentation and add .editorconfig (#973)

.editorconfig

harness/Date_constants.js

harness/PromiseHelper.js

harness/arrayContains.js

harness/assert.js

harness/cth.js

harness/doneprintHandle.js

harness/fnGlobalObject.js

harness/propertyHelper.js

harness/proxyTrapsHelper.js

harness/simdUtilities.js

harness/sta.js

harness/testAtomics.js

harness/testBuiltInObject.js

harness/testIntl.js

harness/timer.js

tools/CoverageAnalyzer.py