[MC-186199] Json data pack validation errors don't show line numbers

The bug

When a file in a data pack has malformed Json, it shows an error including the line number and the path.

com.google.gson.JsonParseException: com.google.gson.stream.MalformedJsonException: Unterminated object at line 9 column 20 path $.pools[0].entries[0].name

However when the Json is valid, but contains another validation error, it doesn't provide this same info. Yet this is vital to debug errors.

com.google.gson.JsonSyntaxException: Expected name to be an item, was unknown string 'minecraft:foo'