ENH: Convert Hunspell Dictionary affix directive parsing else-if chain to switch

[rajat315315]

Description

Issue Description

In org.apache.lucene.analysis.hunspell.Dictionary#readAffixFile, affix directives (such as PFX, SFX, CIRCUMFIX, KEEPCASE, NEEDAFFIX, etc.) were being checked sequentially using a large if-else chain spanning over 120 lines.

The code previously included a TODO comment asking:

// TODO: convert to a switch?

Using a modern Java switch statement on firstWord simplifies this construct, improves code readability, and allows the Java compiler to produce a more efficient bytecode lookup scheme rather than sequential String.equals() comparisons.

Proposed Changes

1. Refactor readAffixFile Directive Parser:

   • Replace the if ("AF".equals(firstWord)) ... else if ... chain in Dictionary.java with a switch (firstWord) statement.
   • Combine multi-label cases sharing identical logic (e.g. "NEEDAFFIX", "PSEUDOROOT" and "ICONV", "OCONV").
   • Removed the stale // TODO: convert to a switch? comment.

2. Refactor Related Directive Helpers:

   • getDecoderAndFlagParsingStrategy: Converted "SET" / "FLAG" header check loop from if-else to switch (firstWord).
   • getFlagParsingStrategy: Refactored if ("num".equals(flagType)) chain to a concise switch expression returning strategy instances.

Benefits

• Readability & Maintainability: Clearer structure and alignment across all Hunspell directive handlers.
• Performance: Better bytecode optimization with tableswitch/lookupswitch over linear string comparisons.
• Code Cleanliness: Resolves existing TODO comment.

Verification

Ran all Hunspell analysis tests:

./gradlew :lucene:analysis:common:test --tests "org.apache.lucene.analysis.hunspell.*"

Result: Build succeeded, all 158 tests passed.