Adding pipeline task aliases. (#11247)

* Adding task aliases and adding `token-classification` and
`text-classification` tasks.

* Cleaning docstring.

tests/test_pipelines_text_classification.py

@@ -17,7 +17,7 @@ import unittest
 from .test_pipelines_common import MonoInputPipelineCommonMixin
 
 
-class SentimentAnalysisPipelineTests(MonoInputPipelineCommonMixin, unittest.TestCase):
+class TextClassificationPipelineTests(MonoInputPipelineCommonMixin, unittest.TestCase):
     pipeline_task = "sentiment-analysis"
     small_models = [
         "sshleifer/tiny-distilbert-base-uncased-finetuned-sst-2-english"

tests/test_pipelines_token_classification.py

@@ -27,7 +27,7 @@ if is_torch_available():
 VALID_INPUTS = ["A simple string", ["list of strings", "A simple string that is quite a bit longer"]]
 
 
-class NerPipelineTests(CustomInputPipelineCommonMixin, unittest.TestCase):
+class TokenClassificationPipelineTests(CustomInputPipelineCommonMixin, unittest.TestCase):
     pipeline_task = "ner"
     small_models = [
         "sshleifer/tiny-dbmdz-bert-large-cased-finetuned-conll03-english"