No warning when EntitySynonymMapper is positioned incorrectly in config.yml

[b-quachtran]

Rasa version: 1.10.3

Rasa SDK version (if used & relevant):

Rasa X version (if used & relevant):

Python version: 3.7.7

Operating system (windows, osx, ...): OS X

Issue:

When EntitySynonymMapper is placed above the entity extractor in config.yml, Rasa will train without throwing any warnings when the component doesn't work as expected.

Error (including full traceback):

Command or request that led to error:

Content of configuration file (config.yml) (if relevant):

# Configuration for Rasa NLU.
# https://rasa.com/docs/rasa/nlu/components/
language: en
pipeline:
  - name: EntitySynonymMapper
  - name: WhitespaceTokenizer
  - name: RegexFeaturizer
  - name: LexicalSyntacticFeaturizer
  - name: CountVectorsFeaturizer
  - name: CountVectorsFeaturizer
    analyzer: "char_wb"
    min_ngram: 1
    max_ngram: 4
  - name: DIETClassifier
    epochs: 100
  - name: ResponseSelector
    epochs: 100

# Configuration for Rasa Core.
# https://rasa.com/docs/rasa/core/policies/
policies:
  - name: MemoizationPolicy
  - name: TEDPolicy
    max_history: 5
    epochs: 100
  - name: MappingPolicy

Content of domain file (domain.yml) (if relevant):