[CodeGen] Add CodeGen model for code generation

[gongel]

PR types

New features

PR changes

Models

Description

• Use example

from paddlenlp.transformers import CodeGenForCausalLM, CodeGenTokenizer

tokenizer = CodeGenTokenizer.from_pretrained('Salesforce/codegen-350M-mono')
model = CodeGenForCausalLM.from_pretrained('Salesforce/codegen-350M-mono')
# Note: left padding for batch input
inputs = tokenizer("def hello_world():", return_token_type_ids=False)
inputs = {k: paddle.to_tensor([v]) for (k, v) in inputs.items()}
output, score = model.generate(**inputs, max_length=128)
print(tokenizer.decode(output[0], skip_special_tokens=True))

[guoshengCS]

LGTM