feat: update the SQLExpression and SQLFragmentHelpers APIs

[wschurman]

Why

The expression API added in #506 was somewhat poisonous. When doing something like jsonPath('fieldName', 'wat').eq(10), the type information was lost due to typescript not carrying it through chains. So I could do something like:

BlahEntity.knexLoader()..loadManyBySQL(sql`${entityField('hadsACat')} = ${true}`)

and it would correctly tell me that the field name is invalid (type info carries into single arg).

But the following wouldn't:

BlahEntity.knexLoader().loadBySQL(expression('hadsACat').eq(true))

How

It's better to just get rid of expression though keep the fluent API on SQLFragmentHelper methods that can carry the type information through the chain.

This PR does a few things:

• adds the required code to carry that type information through
• updates SQLFragmentHelper methods to take either an expression/fragment or entity field name for better usability.
• renames SQLExpression to SQLChainableFragment to better describe what it does
• renames SQLFragmentHelper to SQLExpression to better describe the class of things it contains.

Test Plan

Run new tests.

[wschurman]

• feat: update the SQLExpression and SQLFragmentHelpers APIs #516 👈 (View in Graphite)
• main

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (090c046) to head (cfec837).

Additional details and impacted files

@@            Coverage Diff             @@
##              main      #516    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          110       110            
  Lines        16718     17136   +418     
  Branches      1519      1518     -1     
==========================================
+ Hits         16718     17136   +418     

Flag	Coverage Δ
integration	27.05% <74.21%> (+1.48%)	⬆️
unittest	95.07% <99.43%> (+0.12%)	⬆️

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