Handle `flat` interpolation cases in cross compilation

Fixes #104

- Map HLSL `nointerpolation` to GLSL `flat`

- When lowering a `struct` type varying input/output, look for interpolation modifiers along the "chain" from the leaf field up to the original shader input variable (and take the first one found)
  - Not sure if this is strictly needed, but it seems like a reasonable policy

- Add `flat` to varying input of integer type, with no other interpolation modifier
  - Note: I do *not* do anything to ignore a manually imposed interpolation modifier that might be incorrect

0 files changed, 0 insertions, 0 deletions