Fix compilation with fmt 8.x

Summary:
Fix a bunch of issues that a blocking migration to fmt 8.x:

* Missing includes
* Use of deprecated APIs
* Ambiguous calls to unqualified `format` (can be fmt or folly)
* Unused result of `fmt::format`
* Missing path formatter
* Passing runtime format string

Reviewed By: xavierd

Differential Revision: D33767880

fbshipit-source-id: 3976c4cc0551f3fb42c05a04c29e1c9723245749

folly/test/StringBenchmark.cpp

@@ -120,7 +120,7 @@ BENCHMARK(fmtAppendfBenchmark, iters) {
   for (size_t i = 0; i < iters; ++i) {
     fmt::memory_buffer buf;
     for (size_t j = 0; j < kAppendBufSize; ++j) {
-      fmt::format_to(buf, "{}", 1);
+      fmt::format_to(std::back_inserter(buf), "{}", 1);
     }
     string s = fmt::to_string(buf);
     DCHECK_EQ(s.size(), kAppendBufSize);