## Summary of the Pull Request
Introduces convenience type `til::size` which automatically implements our best practices for size-related types and provides automatic conversions in/out of the relevant types.
## PR Checklist
* [x] In support of Differental Rendering #778
* [X] I work here.
* [x] Tests added/passed
* [x] I'm a core contributor.
## Detailed Description of the Pull Request / Additional comments
- Automatically converts in from anything with a X/Y (console `COORD`) or cx/cy (Win32 `SIZE`)
- Automatically converts out to `COORD`, `SIZE`, or `D2D1_SIZE_F`.
- Constructs from bare integers written into source file
- Default constructs to empty
- Uses Chromium Math for all basic math operations (+, -, *, /)
- Provides equality tests
- Adds initial proposal for division-to-ceiling (round up division) that attempts to `ceil` without any floating point math.
- Accessors for height/width
- Type converting accessors (that use safe conversions and throw) for height/width
- Convenience function for area calculation (as that's common with type) and uses safe math to do it.
- TAEF/WEX Output and Comparators so they will print very nicely with `VERIFY` and `Log` macros in our testing suite.
## Validation Steps Performed
- See automated tests of functionality.
