[FIX] borders: merged cell loses adjacent border after import

[dhrp-odoo]

Description:

Steps to reproduce:

• Apply “All” borders to B2:C3
• Then merge C2:C3

Save the file, close the spreadsheet, and reopen it.

On import, the following happens:

1. From data.borders, we call addBorder with:
   Zone: { top: 1, left: 2, bottom: 2, right: 2 } // C2:C3
   Border: { top, bottom, right, left (all thin black) }

   • This restores the stored borders for the merged range.

2. Then we call addBorder for B2:B3 with:
   Zone: { top: 1, left: 1, bottom: 2, right: 1 } // B2:B3
   Border: { top, bottom, right, left, vertical, horizontal (all thin black) }

   • This reapplies the outer borders on B2:B3.

3. Finally, import() calls addBordersToMerge(), which computes:
   Zone: { top: 1, left: 2, bottom: 2, right: 2 } // C2:C3
   Border: { top, bottom, right } // no left

   and then calls: this.addBorder(sheetId, zone, border, /* force = */ true);

The issue comes from how force was handled inside addBorder().

Because force = true for the merge, every entry in existingBorderSideToClear was set to true.
Thus, when the merged zone was adjacent to B2:B3, we cleared the border on the shared edge even if the new border did not define that side (in this case, there is no left on the merge). As a result, the right border of B2:B3 (the edge between B and C) disappeared after reopening.

We now compute existingBorderSideToClear so that it only depends on the sides actually defined on the new border.

Task: 5390397

review checklist

• feature is organized in plugin, or UI components
• support of duplicate sheet (deep copy)
• in model/core: ranges are Range object, and can be adapted (adaptRanges)
• in model/UI: ranges are strings (to show the user)
• undo-able commands (uses this.history.update)
• multiuser-able commands (has inverse commands and transformations where needed)
• new/updated/removed commands are documented
• exportable in excel
• translations (_t("qmsdf %s", abc))
• unit tested
• clean commented code
• track breaking changes
• doc is rebuild (npm run doc)
• status is correct in Odoo

[robodoo]