[clang-format] PR48539 ReflowComments breaks Qt translation comments

https://bugs.llvm.org/show_bug.cgi?id=48539

Add support for Qt Translator Comments to reflow

When reflown and a part of the comments are added on a new line, it should repeat these extra characters as part of the comment token.

Reviewed By: curdeius, HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D93490

Author: mydeveloperday

clang/lib/Format/BreakableToken.cpp

@@ -41,8 +41,8 @@ static bool IsBlank(char C) {
 
 static StringRef getLineCommentIndentPrefix(StringRef Comment,
                                             const FormatStyle &Style) {
-  static const char *const KnownCStylePrefixes[] = {"///<", "//!<", "///", "//",
-                                                    "//!"};
+  static const char *const KnownCStylePrefixes[] = {"///<", "//!<", "///",
+                                                    "//",   "//!",  "//:"};
   static const char *const KnownTextProtoPrefixes[] = {"//", "#", "##", "###",
                                                        "####"};
   ArrayRef<const char *> KnownPrefixes(KnownCStylePrefixes);

clang/unittests/Format/FormatTestComments.cpp

@@ -702,6 +702,12 @@ TEST_F(FormatTestComments, SplitsLongCxxComments) {
                    "  // long 1 2 3 4 5 6\n"
                    "}",
                    getLLVMStyleWithColumns(20)));
+
+  EXPECT_EQ("//: A comment that\n"
+            "//: doesn't fit on\n"
+            "//: one line",
+            format("//: A comment that doesn't fit on one line",
+                   getLLVMStyleWithColumns(20)));
 }
 
 TEST_F(FormatTestComments, PreservesHangingIndentInCxxComments) {