Allow custom struct args to grad_from_chainrules macro

[mohamed82008]

I noticed that we don't esc the types of the arguments in the @grad_from_chainrules macro. This PR fixes that.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +3.34 :tada:

Comparison is base (65cd309) 81.46% compared to head (30beb59) 84.81%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #232 +/- ## ========================================== + Coverage 81.46% 84.81% +3.34% ========================================== Files 18 18 Lines 1581 1936 +355 ========================================== + Hits 1288 1642 +354 - Misses 293 294 +1 ``` | [Impacted Files](https://app.codecov.io/gh/JuliaDiff/ReverseDiff.jl/pull/232?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaDiff) | Coverage Δ | | |---|---|---| | [src/macros.jl](https://app.codecov.io/gh/JuliaDiff/ReverseDiff.jl/pull/232?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaDiff#diff-c3JjL21hY3Jvcy5qbA==) | `94.33% <100.00%> (+0.69%)` | :arrow_up: | ... and [16 files with indirect coverage changes](https://app.codecov.io/gh/JuliaDiff/ReverseDiff.jl/pull/232/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaDiff)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.

[devmotion]

@mohamed82008 Given https://github.com/JuliaDiff/ReverseDiff.jl/pull/232#discussion_r1266765791, seems the only thing left to do here is maybe addressing https://github.com/JuliaDiff/ReverseDiff.jl/pull/232#discussion_r1266724691?

[mohamed82008]

Thanks @devmotion. I think this is probably good to go.