Move Definition of `I_Tech('REAL4')` to `initialize.m`?

[ranocha]

It seems to be highly unusual to have e.g. I_Tech('REAL') = double and I_Tech('REAL4') = float4. Thus, a bit of code repetition can be avoided. If you agree, @Kostaszki, I can do this after most of the open PRs are (squash-) merged.