The indentNodeProp from @codemirror/lang-yaml computes column-based
indents that produce inconsistent and odd-numbered indentation when
pressing Enter (e.g. 9 spaces after a nested 'web:' line, 6 after a
4-space 'image:' line). Override it with a line-based indentService:
keep the current line's indent, align list-entry keys after the dash
marker, and indent one unit deeper after lines opening a block
(':', '|', '>').
Fixes#4650
7ca96f6087
