fix: default to first declaration for getWellKnownSymbolPropertyOfType properties

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🐛 Bug: getWellKnownSymbolPropertyOfType crashes on a property with no valueDeclaration #15
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

If prop.valueDeclaration doesn't exist, then we assume prop.getDeclarations() must have at least one entry (something must have indicated the property exists!)_.

I don't know that this assumption is actually 100% correct. But it's at least more correct than how the code was before.

[RebeccaStevens]

I don't like the look of those casts.
Do we know for sure that those values are always those types?

[codecov]

Codecov Report

Merging #16 (017a4f0) into main (0c17891) will increase coverage by 2.19%.
The diff coverage is 50.00%.

❗ Current head 017a4f0 differs from pull request most recent head a4664a3. Consider uploading reports for the commit a4664a3 to get more accurate results

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
+ Coverage   19.74%   21.94%   +2.19%     
==========================================
  Files          15       15              
  Lines         395      401       +6     
  Branches      161      164       +3     
==========================================
+ Hits           78       88      +10     
+ Misses        299      291       -8     
- Partials       18       22       +4     

Impacted Files	Coverage Δ
src/types/getters.ts	30.30% <33.33%> (+26.73%)	⬆️
src/nodes/typeGuards/compound.ts	38.09% <100.00%> (+3.09%)	⬆️
src/test/utils.ts	91.66% <100.00%> (ø)
src/nodes/typeGuards/union.ts	1.08% <0.00%> (ø)

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will re-request

[JoshuaKGoldberg]

will re-request

...which I can't do now. The GitHub requests edge cases always confuse me.