[BUG] `case_insensitive` wildcard query didn't return expected result

[HUSTERGS]

Describe the bug

When perform wildcard query on wildcard field with case_insensitive set to true, the expected doc didn't occur.

Related component

Search

To Reproduce

1. Create a simple index contains wildcard field

   PUT case_test
   {
       "mappings": {
           "properties": {
               "wildcard": {
                   "type": "wildcard"
               }
           }
       }
   }
   

2. Bulk insert documents contains capital letters

   PUT _bulk?refresh=true
   {"index": {"_index": "case_test"}}
   {"wildcard": "TtAa"}
   {"index": {"_index": "case_test"}}
   {"wildcard": "ttaa"}
   {"index": {"_index": "case_test"}}
   {"wildcard": "TTAA"}
   

3. Search on wildcard field with case_insensitive set to true and false respectly
   case sensitive:

   POST case_test/_search
   {
       "query": {
           "term": {
               "wildcard": {
                   "value": "TtAa",
                   "case_insensitive": false
               }
           }
       }
   }
   

   case insensitive:

   POST case_test/_search
   {
       "query": {
           "term": {
               "wildcard": {
                   "value": "TtAa",
                   "case_insensitive": true
               }
           }
       }
   }
   

4. Check result

Expected behavior

case insensitive query should return all three documents, instead of TtAa alone

Additional Details

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Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context
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[HUSTERGS]

bugfix is here #15882