[ko] Correct Korean deinflection rules

[Casheeew]

This PR fixes the following issues:

1. The 아/어 form of 이다 is 이어 or 여, this is not reflected correctly in the deinflection rules (it stays the same) (e.g 여서, 이어서 is not deinflected to postpositional particle ida )
   See the wiktionary entry for ida for more info
2. Existing rule -아/어지이다 might be a typo of the -아/어지다 rule. I cannot seem to find any instance of -아/어지이다 on the Internet. -아/어지이다 seems to be an entry in STDict, adding -아/어지다 rule however as it is a common grammatical structure
3. Existing rule -아/아서 is a typo of -아/어서, should be -아/어서
4. The rules for -야 is in regular Korean and not in jamo

This PR also adds tests for those cases.

[Casheeew]

@Lyroxide please review :nanabeg:

[Lyroxide]

looks good