Add case case_sensitive in scandir

[Ezra-Yu]

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Motivation

Some file suffixs are case-insensitive, such as ".JPG" and ".jpg", so add case_sensitive option in scandir. Default True, behave as before.
For example, scandir(root, suffix='JPG', case_sensitive=False) can find pictures with suffix of both ".JPG" and ".jpg" , whilescandir(root, suffix='JPG') can only find pictures with suffix of ".JPG" .

Modification

Add case_sensitive option in scandir. Default True, behave as before.
if set case_sensitive to False, ignore the case of suffix.

BC-breaking (Optional)

No.

Checklist

Before PR:

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

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects, like MMDet or MMCls.
• CLA has been signed and all committers have signed the CLA in this PR.

[CLAassistant]

All committers have signed the CLA.