Describe the bug
CST.setScalarValue() does not preserve non-semantic indentation for block scalars

To Reproduce
Apply setScalarValue() to change the content of a 4-space indented block scalar value in an unindented map. The indentation will be reduced to 2 spaces if afterKey is set, zero otherwise.

Expected behaviour
The original indentation should be kept.

Versions (please complete the following information):

• Environment: node 14.16 / electron 13.5.2 / chrome 91.0.4472.164
• yaml: 2.0.0-10

Additional context
I'm not sure if this is technically a problem with setScalarValue, or with parsing not keeping track of the original indentation relative to the key.