fix(editor): Cmd+X cuts current line and Cmd+A highlights every line on trailing newline (#1075)

[datlechin]

Summary

Two related editor fixes from issue #1075.

Cmd+X cuts the current line when no selection

Matches VS Code, Sublime, JetBrains, and Xcode source editor. New LineCutCalculator (pure, testable) drives the decision in EditorEventRouter:

• With selection → cut the selection (existing behavior preserved).
• No selection → cut the current line including its trailing newline, using NSString.lineRange(for:) (Apple's documented line-boundary API, handles LF / CR / CRLF correctly).
• No-op cases: empty buffer, cursor past end, cursor at the trailing-empty position with no preceding line.

Cmd+A highlights every line, not just the first, on trailing-newline buffers

In TextSelectionManager+FillRects.swift, the else branch was wrongly entered for the LAST text line whenever intersectionRange.max == lineStorage.length, and rectForOffset(lineStorage.length) resolved to the trailing-empty-line position at the leading edge — collapsing the highlight to width 0.

Fix: detect when the line ends with a line-break character via LineEnding(line:) and treat that case the same as a non-end-of-doc line — extend the highlight to the right edge.

Reproduced in unit test before the fix:

Buffer: "select * from users;\nselect * from users;\n"  (length 42)
Before fix → fill rects:
  [0] x=0 w=1000  ← line 1 highlighted ✓
  [1] x=0 w=0     ← line 2 INVISIBLE ✗
After fix → both lines have w=1000.

Test plan

• TableProTests → LineCutCalculatorTests (13 tests) all pass.
• CodeEditTextViewTests → SelectAllWithTrailingNewlineTests (13 tests) all pass.
• CodeEditTextViewTests → CmdShiftLeftAtEndOfDocumentTests (9 regression tests) all pass.
• Manual SQL editor:
  • Type a single line, place cursor anywhere, Cmd+X → entire line cut to clipboard.
  • Multi-line, cursor on middle line, Cmd+X → that line + trailing \n cut, lines below shift up.
  • Make a selection, Cmd+X → only the selection is cut (no regression).
  • Cmd+C with selection still works.
  • Type a query ending with \n (extra empty line at the bottom). Cmd+A → every line shows blue highlight, including the one before the trailing empty line.
  • Type a query NOT ending with \n. Cmd+A → every line highlighted, last line's highlight stops at the text end (no extension to right edge).

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