Support multi-line decorations in the minimap

[mjbvz]

Testing #76030

Repo

1. Enable minimap
2. Open a file
3. Search for \n with regular expressions enabled

bug
The entire minimap becomes orange:

[gregvanl]

Yep, something odd with \n and regex. If you search for text with trailing \n, the minimap shows the beginning non-matching part of the line highlighted, not the actual matched string.

[RMacfarlane]

Nice catch! I'm not correctly handling multi-line decorations. Will defer this to next iteration, since the I think the fix will be more involved