FEAT: Specify input product using producer name

[beojan]

This is a preliminary solution for #108. Output products still need to be specified as empty strings at this point.

The API for input product specification without a product name is:

.input_products(from(producer_name).in(layer_name), ...)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #184      +/-   ##
==========================================
+ Coverage   81.13%   81.46%   +0.33%     
==========================================
  Files         116      116              
  Lines        2083     2083              
  Branches      332      331       -1     
==========================================
+ Hits         1690     1697       +7     
+ Misses        255      250       -5     
+ Partials      138      136       -2     

Flag	Coverage Δ
unittests	81.46% <100.00%> (+0.33%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
phlex/core/edge_creation_policy.hpp	100.00% <ø> (+18.18%)	⬆️
phlex/core/product_query.cpp	66.66% <100.00%> (+2.38%)	⬆️
phlex/core/product_query.hpp	66.66% <100.00%> (+4.16%)	⬆️

... and 2 files with indirect coverage changes

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