[formatv][FmtAlign] Use fill count of type size_t instead of uint32_t (#78459)

FmtAlign::fill() accepts a uint32_t variable while the usages operate on
size_t values. On some platform / compiler combinations, this ends up
being a narrowing conversion. Fix this by changing the function's signature.
This was first seen on MSVC x86.

Co-authored-by: Orest Chura <[email protected]>

Author: andrey-golubev

llvm/include/llvm/Support/FormatCommon.h

@@ -66,8 +66,8 @@ struct FmtAlign {
   }
 
 private:
-  void fill(llvm::raw_ostream &S, uint32_t Count) {
-    for (uint32_t I = 0; I < Count; ++I)
+  void fill(llvm::raw_ostream &S, size_t Count) {
+    for (size_t I = 0; I < Count; ++I)
       S << Fill;
   }
 };