fix(@aws-amplify/datastore): Fix beginsWith() negation

[svidgen]

Description of changes

Fixes an issue where the absence of special handling for the negation of beginsWith resulted in an error for queries like this:

await DataStore.query(Model, m => m.not(m => m.field.beginsWith('anything')));

This fix would be a reasonable amount more difficult to figure out and grok using the existing storage predicate builder that V5 predicates was still using in some places. So, this PR pulls forward a refactor from #10949 around storage predication generation to make the fix sane and simple.

A component of that refactor is a fix to IndexedDBAdapter's determination of whether a predicate is a "key value predicate". I'm not sure clear on where the storage predicate builder handles null conditions, but IndexedDB throws a fit if you try to index.get([null]). For this refactor, I've opted explicitly handle this on the IndexedDBAdapter side, because issue only seems to affect IndexedDB.

Issue #, if available

#10957

Description of how you validated changes

1. Added negation tests for each of our string matches.
2. Saw the beginsWith negation test fail.
3. Made it pass.

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

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

[codecov-commenter]

Codecov Report

Merging #10962 (a20f80a) into main (7da8e64) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main   #10962      +/-   ##
==========================================
- Coverage   81.59%   81.55%   -0.04%     
==========================================
  Files         198      198              
  Lines       19609    19610       +1     
  Branches     4232     4237       +5     
==========================================
- Hits        15999    15993       -6     
- Misses       3319     3327       +8     
+ Partials      291      290       -1     

Impacted Files	Coverage Δ
packages/datastore/src/predicates/next.ts	94.94% <100.00%> (+0.30%)	⬆️
.../datastore/src/storage/adapter/IndexedDBAdapter.ts	89.07% <100.00%> (+0.11%)	⬆️
packages/datastore/src/predicates/index.ts	78.86% <0.00%> (-9.76%)	⬇️
packages/datastore/src/util.ts	95.90% <0.00%> (+0.86%)	⬆️

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