Fix #1390: preserve line breaks and whitespace in FileSystemConfigSource

sources/file-system/src/main/java/io/smallrye/config/source/file/FileSystemConfigSource.java

@@ -97,11 +97,7 @@ private static Map<String, String> scan(File directory) {
     }
 
     private static String readContent(Path file) {
-        try (Stream<String> stream = Files.lines(file)) {
-            return stream.collect(Collectors.joining());
-        } catch (IOException e) {
-            throw new UncheckedIOException(e);
-        }
+        return Files.readString(file);
     }
 
     @Override

sources/file-system/src/test/java/io/smallrye/config/source/file/FileSystemConfigSourceTest.java

@@ -57,4 +57,13 @@ void testCharacterReplacement() throws URISyntaxException {
         // you can't rewrite the key, only the file name
         assertNull(configSource.getValue("MYSERVICE_MP_REST_URL"));
     }
+
+    @Test
+    void testMultilineValue() throws URISyntaxException {
+        URL configDirURL = this.getClass().getResource("configDir");
+        File dir = new File(configDirURL.toURI());
+
+        ConfigSource configSource = new FileSystemConfigSource(dir);
+        assertEquals("line 1\n\n   \nline with trailing spaces   \n\n", configSource.getValue("foo"));
+    }
 }

sources/file-system/src/test/resources/io/smallrye/config/source/file/configDir/foo

@@ -0,0 +1,5 @@
+line 1
+
+
+line with trailing spaces   
+