[lldb] Use std::size instead of llvm::array_lengthof

LLVM contains a helpful function for getting the size of a C-style
array: `llvm::array_lengthof`. This is useful prior to C++17, but not as
helpful for C++17 or later: `std::size` already has support for C-style
arrays.

Change call sites to use `std::size` instead.

Differential Revision: https://reviews.llvm.org/D133501

lldb/source/Plugins/ObjectFile/PECOFF/ObjectFilePECOFF.cpp

@@ -743,7 +743,7 @@ bool ObjectFilePECOFF::ParseSectionHeaders(
 }
 
 llvm::StringRef ObjectFilePECOFF::GetSectionName(const section_header_t &sect) {
-  llvm::StringRef hdr_name(sect.name, llvm::array_lengthof(sect.name));
+  llvm::StringRef hdr_name(sect.name, std::size(sect.name));
   hdr_name = hdr_name.split('\0').first;
   if (hdr_name.consume_front("/")) {
     lldb::offset_t stroff;