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.
## Summary of the Pull Request
<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist
* [x] Closes#4013
* [x] I work here.
* [x] Existing tests should be OK. Real changes, just adding a lib to use.
* [x] Couldn't find any existing docs about intsafe.
* [x] Am core contributor.
## Detailed Description of the Pull Request / Additional comments
* [x] Can we remove min/max completely or rename it in the two projects where it had to be reintroduced? This is now moved into #4152
* [x] How many usages of the old safe math are there? **79**
* [x] If not a ton, can we migrate them here or in a follow on PR? This is now moved into #4153
Files with old safe math:
- TerminalControl: TSFInputControl.cpp
- TerminalCore: TerminalDispatch.cpp
- TerminalCore: TerminalSelection.cpp
- Host: directio.cpp
- RendererGdi: invalidate.cpp
- RendererGdi: math.cpp
- RendererGdi: paint.cpp
- RendererVt: paint.cpp
- TerminalAdapter: adaptDispatch.cpp
- Types: viewport.cpp
- Types: WindowUiaProviderBase.cpp
## Validation Steps Performed
