[clang] [llvm] [clang-format]: Add `Custom` to `ShortFunctionStyle`; add new AllowShortFunctionsOnASingleLineOptions for granular setup (PR #134337)

[Owen Pan via llvm-commits]

================
@@ -622,15 +622,26 @@ template <> struct ScalarEnumerationTraits<FormatStyle::ShortBlockStyle> {
   }
 };
 
-template <> struct ScalarEnumerationTraits<FormatStyle::ShortFunctionStyle> {
-  static void enumeration(IO &IO, FormatStyle::ShortFunctionStyle &Value) {
-    IO.enumCase(Value, "None", FormatStyle::SFS_None);
-    IO.enumCase(Value, "false", FormatStyle::SFS_None);
-    IO.enumCase(Value, "All", FormatStyle::SFS_All);
-    IO.enumCase(Value, "true", FormatStyle::SFS_All);
-    IO.enumCase(Value, "Inline", FormatStyle::SFS_Inline);
-    IO.enumCase(Value, "InlineOnly", FormatStyle::SFS_InlineOnly);
-    IO.enumCase(Value, "Empty", FormatStyle::SFS_Empty);
+template <> struct MappingTraits<FormatStyle::ShortFunctionStyle> {
+  static void enumInput(IO &IO, FormatStyle::ShortFunctionStyle &Value) {
+    IO.enumCase(Value, "None", FormatStyle::ShortFunctionStyle({}));
----------------
owenca wrote:

```suggestion
    IO.enumCase(Value, "None", FormatStyle::ShortFunctionStyle());
```
Ditto below and in other files as well.

https://github.com/llvm/llvm-project/pull/134337