Add a helper file to resolve merge conflicts

I'm not sure how to integrate this into our merging code.

lib/utils/merge_conflict_resolver.dart

@@ -0,0 +1,36 @@
+import 'dart:convert';
+
+String resolveMergeConflict(String fileContents) {
+  var lines = const LineSplitter().convert(fileContents);
+  var newLines = <String>[];
+
+  var inMergeConflict = false;
+  var seenStartMarker = false;
+  var seenMiddleMarker = false;
+
+  lines.forEach((line) {
+    if (line.startsWith("<<<<<<<") && !inMergeConflict) {
+      inMergeConflict = true;
+      seenStartMarker = true;
+      return;
+    }
+    if (line == "=======" && inMergeConflict && seenStartMarker) {
+      seenMiddleMarker = true;
+      return;
+    }
+    if (line.startsWith(">>>>>>>") && inMergeConflict && seenMiddleMarker) {
+      inMergeConflict = false;
+      seenStartMarker = false;
+      seenMiddleMarker = false;
+      return;
+    }
+
+    if (inMergeConflict && seenMiddleMarker) {
+      return;
+    }
+
+    newLines.add(line);
+  });
+
+  return newLines.join('\n');
+}

test/merge_conflcts_resolver_test.dart

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+import 'package:test/test.dart';
+import 'package:gitjournal/utils/merge_conflict_resolver.dart';
+
+void main() {
+  test("Body only conflict", () {
+    String input = '''---
+title: Foo
+---
+
+<<<<<<< HEAD
+This is the body in GitJournal
+=======
+This is the body from the remote/origin
+>>>>>>> remote/origin
+
+Some more text.''';
+
+    String expectedOutput = '''---
+title: Foo
+---
+
+This is the body in GitJournal
+
+Some more text.''';
+
+    expect(resolveMergeConflict(input), equals(expectedOutput));
+  });
+
+  /*
+  test("YAML Conflict", () {});
+  test("YAML Conflict from 1st line", () {});
+  test("YAML Conflict different modified", () {});
+  test("YAML and body conflict", () {});
+  */
+}