Error for missing anchor (unidentified alias) broken since 1.0

[vtcifer]

Describe the bug

If you make use of an alias which has no corresponding anchor, this extension used to provide an error (version 0.23 and before).
Since version 1.0 and beyond, no error is generated.

Expected Behavior

An error should be listed in the 'Problems' window.

Version 0.23:

Current Behavior

No error is generated.

Steps to Reproduce

1. Set yaml.yamlVersion to 1.1.
2. Create a yaml file with the following content:

bar: *bar
baz: 
  <<: *baz

Environment

• Windows
• Mac
• Linux
• other (please specify)

[msivasubramaniaan]

Till 0.23.0 we used js-yaml and from version 1.0.0 we replaced with yaml npm. As no schema is enforced, it may not detect any errors and it simply parsed as string.