[llvm] [APFloat] Add APFloat::format (PR #99088)

[Matt Arsenault via llvm-commits]

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@@ -1378,6 +1378,171 @@ TEST(APFloatTest, toString) {
   }
 }
 
+TEST(APFloatTest, format) {
+  auto doit_precision = [](const fltSemantics &S, const char *value,
+                           llvm::FloatStyle style, int precision,
+                           const char *expected) {
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arsenm wrote:

```suggestion
                           StringRef expected) {
```

https://github.com/llvm/llvm-project/pull/99088