Fix shadow variables

[JohanBertrand]

More details in nasa/fprime#2482

Fixes in the code generation to remove -Wshadow warnings:

• Added m_ for fprime component member variables

[LeStarch]

I see what I expect....but it seems like certain models where updated. I like those changes, but will defer to @bocchino to determine if they are desired.

[bocchino]

Looks good! I reverted two changes: (1) I restored the old behavior of the toString conversion. The names of the logical struct variables are the names shown in FPP. The m_ names are only for the C++ implementation. (2) I restored the FPP variable names in the unit tests.

[JohanBertrand]

Thanks!

I originally changed the names of the variables in the fpp files, because I thought we should not advise users to add a m prefix in front of the variables they defined.

[bocchino]

I think it's OK in the context of a unit test. In real code, a struct member name should say what the member does. In a unit test context, it seems fine to call a U32 member mU32, since it really has no purpose except to be a U32 member in the context of that test.