Avoid inlining error reporting in checked_convert (#66721)
Summary:
**Summary:** Move the error reporting part to the cpp file to avoid callers inlining it, which inflates the generated code size. See https://github.com/pytorch/pytorch/issues/65830.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66721
Test Plan:
Compiling the simple program below now generates ~150 lines of assembly, compared to 700+ lines before.
```
#include <c10/core/Scalar.h>
void g(float) {}
void f(const c10::Scalar& scalar) {
auto x = scalar.to<float>();
g(x);
}
```
**Reviewers:** Brian Hirsh
**Subscribers:** Brian Hirsh, Edward Yang, Yining Lu
**Tasks:** T103384490
**Tags:** pytorch
Fixes https://github.com/pytorch/pytorch/issues/65830
Reviewed By: zou3519, bdhirsh
Differential Revision: D31737607
Pulled By: andrewor14
fbshipit-source-id: 3d493c4d8e51d8f8a19d00f59b8ea28176c8a9e3
