Adjust MA0007 trailing comma behavior for collection expressions

[meziantou]

MA0007 currently reports on multiline collection expressions even when the last element is directly followed by the closing bracket on the same line. This produces noise for common spread-element formatting.

This change updates MA0007 so collection expressions only require a trailing comma when the closing ] is on a later line than the last element. If the last element and ] are on the same line, no diagnostic is reported.

It also adds focused C# 12 tests for:

• same-line closing bracket cases (with and without preceding values)
• next-line closing bracket cases
• a trailing comment before the closing bracket on the next line

Finally, the MA0007 rule documentation is updated to describe the new default behavior for collection expressions.

Fix #1126