Clear stale isWrapped when resize skips reflow for cursor line

[dolonet]

Fixes #3482.

What

When resizing to a wider terminal, _reflowLarger skips merging a wrapped-line group if the cursor is inside that group — the comment already notes that "the program will handle fixing up wrapped lines with the cursor". But the wrapped rows keep isWrapped = true even though their content no longer wraps in the new width. Any consumer of isWrapped (triple-click selection is the user-visible symptom in the issue) then treats the now-visually-separate rows as a single logical line.

Fix

Inside the cursor-skip branch, clear isWrapped on any continuation row whose predecessor no longer fills the new last column. The predecessor's last cell has already been null-padded by the pre-reflow line resize, so hasContent(newCols - 1) is a reliable signal that the wrap cannot exist at the new width.

Content on the cursor line is deliberately left alone — only the flag is cleaned up, matching the "program will fix up" contract.

Repro

Before:

cols=5, two rows "aaaaa" / "bbbbb" (isWrapped=true), cursor inside group
→ resize cols=10 → line0="aaaaa     " line1="bbbbb     " isWrapped=true (stale)
→ triple-click selects both rows

After: line1.isWrapped === false; triple-click selects only one row.

Test

Added should clear stale isWrapped when the cursor is on a wrapped line and reflow is skipped (#3482) in Buffer.test.ts.