Replace fs-extra ensureFile with fs.mkdir and fs.writeFile

Replaces fs-extra's ensureFile/createFile (and their Sync variants) with mkdir(dirname(file), { recursive: true }) followed by writeFile(file, '', { flag: 'a' }), which creates the file without truncating an existing one. A call standing alone as a statement becomes two statements; other promise-form calls chain the two with .then. A path that isn't safe to evaluate twice is hoisted into a const first, which needs a statement to sit before, so such a call in expression position is left alone, as are callback-form calls and sync calls used as expressions.