Implements the make_field system macro

[zslayton]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Attention: Patch coverage is 75.97403% with 37 lines in your changes missing coverage. Please review.

Project coverage is 77.81%. Comparing base (4ac3e78) to head (6db49c5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lazy/expanded/macro_evaluator.rs	75.65%	19 Missing and 9 partials ⚠️
src/lazy/expanded/struct.rs	75.00%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #878      +/-   ##
==========================================
+ Coverage   77.79%   77.81%   +0.01%     
==========================================
  Files         136      136              
  Lines       34533    34656     +123     
  Branches    34533    34656     +123     
==========================================
+ Hits        26864    26966     +102     
- Misses       5678     5690      +12     
- Partials     1991     2000       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jobarr-amzn]

Suggested change

	// For any other kind of struct, do a linear scan over its fields until we encounter
	// one with the requested name.
	// For any other kind of struct (e.g. struct literal or make_struct call),
	// do a linear scan over its fields until we encounter one with the requested name.

I like a reminder of what the other cases are. It doesn't have to come this way.

[zslayton]

I'm going to incorporate this in another PR I'm about to open.