`MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS` should work for enum as keys

[XakepSDK]

Describe the bug
ACCEPT_CASE_INSENSITIVE_ENUMS not working for enums as map keys

Version information
2.11.2

To Reproduce
Use enum as map key and deserialize json with different key case

Expected behavior
ACCEPT_CASE_INSENSITIVE_ENUMS works for map enum keys

[ILGO0413]

I would like to work on it.

[ILGO0413]

According to README.md#Basic rules for Code Contributions, I should provide a filled Contributor License Agreement. Do you have any example of CLA?

[cowtowncoder]

@ILGO0413 yes, it's under "FasterXML/jackson" repo:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

and the easiest way is probably to print, fill & sign, scan/photo, email to info at fasterxml dot com.

[ILGO0413]

Would you accept it if I write it by hand?

[cowtowncoder]

CLA as submitted fine (i.e. electronic variant works for us). Thank you for doing it very quickly!