[clang] [clang-format] Add KwBreakBeforeCaseLabel (PR #227668)

[Anan Yablonko via cfe-commits]

================
@@ -2833,6 +2833,42 @@ TEST_F(FormatTest, FormatsSwitchStatement) {
                Style);
 }
 
+TEST_F(FormatTest, FormatsSwitchStatementCompactCaseLabels) {
----------------
ananski-the-3rd wrote:

[[fallthrough]] is now handled.

I added a couple of tests that check interaction with options that appear in UnwrappedLineParser::parseLabel.

As for the options you specified, I'd like to verify what the intended interaction is.
I suggest these (currently all failing) tests as a start:
```cpp
  Style.BreakAfterAttributes = FormatStyle::ABS_Always;
  verifyFormat("switch (n) {\n"
               "  break; case 0:\n"
               "    foo();\n"
               "    [[fallthrough]];\n"
               "  case 1:\n"
               "    bar();\n"
               "}",
               "switch (n) {\n"
               "  break; case 0:\n"
               "    foo();\n"
               "  [[fallthrough]]; case 1:\n"
               "    bar();\n"
               "}",
               Style);

  Style.AllowShortCaseLabelsOnASingleLine = true;
  Style.AlignConsecutiveShortCaseStatements.Enabled = true;
  verifyFormat("switch (n) {\n"
               "  break; case 0:  b = false;\n"
               "  break; default: b = true;\n"
               "}",
               Style);

  Style.ColumnLimit = 54;
  verifyFormat("switch (n) {\n"
               "  break; case some_namespace::\n"
               "      some_constant:\n"
               "    b = false;\n"
               "  break; default:"
               "    b = true;\n"
               "}",
               Style);
```

Is this acceptable as intended behavior?

https://github.com/llvm/llvm-project/pull/227668