[add] ConcatDataset.evaluate feature

[17862923747]

Motivation

多数据集场景，val时会报错，因为您的ConcatDataset.evaluate没有实现

Modification

我补充了缺少的这部分代码：ConcatDataset.evaluate

BC-breaking (Optional)

可兼容已有代码和config

Use cases (Optional)

Checklist

Before PR:

• [x] I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• [x] Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• [x] Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• [x] New functionalities are covered by complete unit tests. If not, please add more unit tests to ensure correctness.
• [x] The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• [x] CLA has been signed and all committers have signed the CLA in this PR.

[CLAassistant]

All committers have signed the CLA.

[ly015]

@17862923747 Hi, thank you very much for your help! Could you please sign the CLA so we can accept your contribution? This PR will be reviewed asap.

[Ben-Louis]

@17862923747 您好，请问您还有更新这个 PR 的计划吗？如果有任何困难，我们也可以帮助您一起完善这个 PR 的内容

[OpenMMLab-Assistant001]

Hi @17862923747 ！We are grateful for your efforts in helping improve this open-source project during your personal time.

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