Adds non-reserved keywords (POC)

[johnedquinn]

Relevant Issues

• Related to Initializes non-reserved PartiQL keywords partiql-lang-kotlin#780. It is marked as a draft pending an RFC.

Description

• This is a proof of concept (POC) for adding non-reserved keywords to the Rust implementation
• I've added several keywords to the NonReservedKeywords list in LALRPOP
  • ACYCLIC, BOTH, DOMAIN, LEADING, TRAIL, TRAILING, and USER to match the PR linked above
  • Also added ORDER, but this is only because ORDER is already used within Rust's grammar as a keyword -- and I wanted to show how existing keywords can be converted to non-reserved keywords.
• I also modified the preprocessor so that it can parse TRAILING, LEADING, and BOTH appropriately.
• If they can be parsed as VarRefExprs, we convert them to SymbolPrimitives (case-insensitive), so we don't even need to know what their original case is. I didn't add qualified/unqualified to this PR, as it's a quick POC.
• I've added tests to show several scenarios of using non-reserved keywords.
• I don't intend for this to be merged, as I am not familiar with the codebase -- however I wanted to show how it can possibly be done.
• Note: I'm unfamiliar with this language, so please excuse mistakes made along the way

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

[codecov]

Codecov Report

Base: 86.28% // Head: 86.72% // Increases project coverage by +0.43% 🎉

Coverage data is based on head (489c9f7) compared to base (a279276).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #221      +/-   ##
==========================================
+ Coverage   86.28%   86.72%   +0.43%     
==========================================
  Files          31       31              
  Lines        5074     5226     +152     
==========================================
+ Hits         4378     4532     +154     
+ Misses        696      694       -2     

Impacted Files	Coverage Δ
partiql-parser/src/lexer.rs	98.34% <100.00%> (+0.08%)	⬆️
partiql-parser/src/parse/mod.rs	95.21% <100.00%> (+0.37%)	⬆️
partiql-parser/src/preprocessor.rs	94.47% <100.00%> (+1.63%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[github-actions]

Conformance comparison report

	main (a279276)	e3a3e60	+/-
% Passing	12.65%	12.65%	0.00%
✅ Passing	349	349	0
❌ Failing	0	0	0
🔶 Ignored	2410	2410	0
Total Tests	2759	2759	0

Number passing in both: 349

Number failing in both: 0

Number passing in main but now fail: 0

Number failing in main but now pass: 0

[jpschorr]

These tests all pass without any of the above parser changes, except for with_order (thought I think the gpml tests would fail when the gpml parsing rules are included).

I'm also not sure that i feel treating order as an unreserved keyword is a good idea...