Implement commonly used Excel functions that are missing from Google Sheets

[Jython1415]

ISOMITTED, for example.

We would need to come up with a comprehensive list and break it into subissues first.

[Jython1415]

Progress Update

Significant progress has been made on implementing Excel functions. Here's the current status:

✅ Completed (9 functions)

• Implement TEXTAFTER function #53 TEXTAFTER - Extract text after delimiter
• Implement TEXTBEFORE function #54 TEXTBEFORE - Extract text before delimiter
• Implement TEXTSPLIT function #55 TEXTSPLIT - Split text into array (1D version)
• Implement EXPAND function #57 EXPAND - Expand/pad arrays to dimensions
• Implement TRIMRANGE function #58 TRIMRANGE - Remove empty rows/columns from edges
• Implement PERCENTOF function #60 PERCENTOF - Calculate percentage contribution
• Implement SINGLE function #63 SINGLE - Extract value from array intersection
• Implement DROP function #56 DROP - Already implemented
• (Several others from earlier work)

❌ Closed as Not Planned (3 functions)

• Implement SORTBY function #62 SORTBY - Native SORT already provides this
• Implement VALUETOTEXT function #64 VALUETOTEXT - Low priority
• Implement ARRAYTOTEXT function #65 ARRAYTOTEXT - Low priority

🔄 Open Issues Requiring Decision (2 functions)

• Implement AGGREGATE function #59 AGGREGATE - Blocker: Cannot detect hidden rows in Google Sheets (core feature). Recommend closing/deferring.
• Implement ISOMITTED function #61 ISOMITTED - Workaround exists using empty argument detection pattern, but requires user discipline. Recommend documenting pattern vs implementing function.

📊 Summary

• Implemented: 9+ functions
• Not Planned: 3 functions (low value or redundant)
• Pending Decision: 2 functions (platform limitations)
• Recent PR: Implement 6 new Excel functions for Google Sheets #124 implemented 6 functions in one batch

The Excel function initiative is largely complete. Recommend reviewing #59 and #61 to determine next steps.

[Jython1415]

Closing as most of them have been implemented, and the remaining issues (#59 and #61) and be standalone.