Converts the poly text out string and width buffers to use a memory pool since we free/alloc those every frame and are just going to reuse them over and over.
## PR Checklist
* [x] Supports #3075
* [x] I work here.
* [x] Profiled memory before/after. Tested manually with `big.txt`.
## Detailed Description of the Pull Request / Additional comments
- Sets up a PMR memory pool for the GDI Engine. It tends to alloc and free a bunch of little buffers during painting frames. The pool will likely hold onto that memory frame over frame, but we'd just be using it again and again and again anyway. So this way we avoid all the system memory allocator locks and syscalls.
## Validation Steps Performed
- Ran `big.txt` about 10x in the window. Checked WPR/WPA profile output before/after.
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