Support `tag:yaml.org,2002:merge` for parsing `!!merge <<: &foo`

[dastrobu]

Is your feature request related to a problem? Please describe.

In short, please add support for tag:yaml.org,2002:merge for parsing !!merge <<: &foo.

Parsing the following yaml

const YAML = require('yaml')

YAML.parse(`
      foo: &foo
       a: 1
       b: 2
      bar:
       !!merge <<: *foo
`, {merge: true})

results in a warning

 (node:28408) [TAG_RESOLVE_FAILED] YAMLWarning: Unresolved tag: tag:yaml.org,2002:merge at line 6, column 8:

      bar:
       !!merge <<: *foo
       ^^^^^^^

While

YAML.parse(`
      foo: &foo
       a: 1
       b: 2
      bar:
       <<: *foo
`, {merge: true}) 

works fine.

Describe the solution you'd like

Parsing works without warning.

Describe alternatives you've considered

My workaround is currently adding the following custom tag:

const YAML = require('yaml')

const mergeTag = {
  tag: 'tag:yaml.org,2002:merge',
  resolve(value) {
    return value;
  }
};

YAML.parse(`
      foo: &foo
       a: 1
       b: 2
      bar:
       !!merge <<: *foo
`, {merge: true, customTags: [mergeTag]})

which basically ignores the tag (if I am not mistaken).

Additional context

The problem came up, since yq is creating these tags automatically, when patching a yaml with a merge. Here is an example

echo ' 
foo: &foo
  a: 1
  b: 2
bar:
   <<: *foo'  | 
yq '.foo.a |= "b"'

which results in

foo: &foo
  a: b
  b: 2
bar:
  !!merge <<: *foo

note the inserted !!merge.