When using the parser to do static analysis and editor integrations, it's
still useful to be able to get the incomplete AST resulting from a parse
error.
Callers that intend to use the returned value to take real actions (as
opposed to just analysis) must check diags.HasError() to determine if
the returned file can be considered valid.
We need to be careful to keep straight the distinction between JSON
properties and zcl body attributes here, since properties can represent
both attributes _and_ blocks.
This is a wrapper around Body.PartialContent that generates additional
error diagnostics if any object properties are left over after decoding,
helping the config author to catch typos that would otherwise have caused
a property to be silently ignored.
Even if errors were encountered during parsing, it is helpful to still
return a partial AST if possible since that allows for the source code
analysis features to still (partially) work in the face of errors.
Currently lacking correct support for unicode text segmentation into
grapheme clusters, so it miscounts "Column" in positions. This will be
addressed later.
