fix: toolbox search final trigram

[goughjo02]

The basics

• I validated my changes

The details

Resolves

Fixes #2645

Proposed Changes

• Include the final trigram when generating search tokens to prevent partial matches on long queries.
• Add a regression test covering the “conso” false positive case.
• Expand BlockSearcher tests for short/empty input, underscore normalization, dropdown alt text indexing, and disambiguation between similar blocks.

Reason for Changes

• Prevent toolbox search from returning false positives for queries longer than three characters and improve overall search accuracy.

Test Coverage

• npm test -- --runInBand (blockly-scripts test)

Documentation

• No documentation updates needed.

Additional Information

• Additional tests define temporary blocks/dropdowns to exercise edge cases; no user-facing behavior changes beyond correcting search results.