[DirectX] Implement Shader Flags Analysis for DX11_1_DoubleExtensions

[bharadwajy]

Currently all instructions except the following case are inspected to determine if DX11_1_DoubleExtensions flag is to be set.

Set function-level flag DX11_1_DoubleExtensions flag if the function calls DXIL::Opcode::Fma.

This flag is named m_bEnableDoubleExtensions in dxc sources.

AC:

Add tests to verify the flag is set.

[Icohedron]

This is blocked on #99117