#2383 - Fixed issue where VLOOKUP and HLOOKUP sometimes returned wrong value on unsorted data.

[swmal]

Summary

Fixes VLOOKUP and HLOOKUP with approximate match (range_lookup = TRUE or
omitted) returning results that differ from Excel, including the case reported in
issue 1054.

Problem

The approximate-match binary search did not run over the range as given. It first
trimmed the range to a value sub-range and removed all blank cells before searching.
This shifted the binary search midpoints relative to Excel, producing wrong results
(sometimes 0 or an incorrect row) on ranges containing blank cells — both sorted
data with gaps and unsorted data.

Fix

Approximate match now performs a plain binary search over the whole range, exactly
like Excel:

• No trimming and no removal of cells. Blank cells keep their original positions, so
  the midpoint sequence matches Excel's.
• A blank cell encountered at a midpoint is skipped forward to the next value to get a
  comparison direction (Excel sees past blanks). This scan is bounded by the position
  of the last value, so a whole-column reference (e.g. A:A) never scans across the
  empty remainder of the column — the lookup stays O(log n).
• A non-comparable header in the first value position is handled as before.

This is implemented in LookupBinarySearch.SearchAscFullRange; VLookup and
HLookup call it for the approximate-match path.

Tests

Added coverage for approximate match with blank cells in leading, inner, and trailing
positions (vertical and horizontal), unsorted data, and a whole-column reference where
the data sits far above the empty tail.

Note

For unsorted data, approximate match is not standardised in Excel and the result
depends on the exact binary search path. This change makes EPPlus follow Excel's
search over the range, but exact parity on arbitrary unsorted data cannot be
guaranteed.