Add Fortran test using activity descriptors

[joewallwork]

Closes #2862
Merges into #2837

Adds the norm example from the Enzyme tutorial https://github.com/EnzymeAD/Enzyme-Tutorial/tree/main/2_norm with variants under ifx and flang.

[joewallwork]

Well this is upsetting
https://community.intel.com/t5/Intel-Fortran-Compiler/symbol-E-missing-in-output-of-real-numbers-with-E0-or-ES0-format/m-p/1310862
Under the scientific notation format specifier es0.0, IFX writes 1.-06, whereas every other Fortran compiler I've used would write 1.E-06. For now we can just have different checks because the two variants of the norm example are currently run with two different compilers (see ad68e03). However, eventually we'll need to align this. A few options:

1. Add custom lit CHECK commands for different compilers (prefer not)
2. Use #ifdef __INTEL_COMPILER etc (prefer not)
3. Change what's being printed to avoid the issue, e.g., scale by 1e6 (preferable?)

[vchuravy]

Yeah let's go with 3

[joewallwork]

Yeah let's go with 3

Done in f084c97.

[joewallwork]

To finish this example, I need to teach Enzyme how to differentiate the Fortran intrinsic sum (i.e. _FortranASumReal4) and also the _FortranAAssign that it sees in the LLVM.

[vchuravy]

Suggestion from meeting: Choose a different test for this that doesn't require an intrinsic.

[joewallwork]

Closing as superseded by #2917.