{fmt} 7.1.3 includes a number of changes, which I will summarize here:
* Switched to Dragonbox for float formatting (quoted, "20-30x faster"
than ostringstream)
* Significantly improves `FMT_COMPILE` (compile-time format string)
{fmt} 7.0.1 improves binary size, compile-time format string handling,
compile time improvements and named arguments.
In a test Windows build, it shrank our binary by ~14kb.
Closes#6905.
## PR Checklist
* [x] Closes#6905
* [x] CLA
This change is necessary as the dep/ folder is not synced into the
Windows source tree.
I've also added a build rule producing a lib for {fmt}.
This will be required for our next OS ingestion.
