[Doris On ES][Bug] When multi fields with `text` type, query ES table would fails

[hexian55]

Describe the bug
MappingPhase.resolveKeywordFields put null value in fetchFieldsContext

To Reproduce
Steps to reproduce the behavior:

1. es index mapping
   {
   "test": {
   "mappings": {
   "properties": {
   "k1": {
   "type": "long"
   },
   "k2": {
   "type": "keyword"
   },
   "k3": {
   "type": "text",
   "fields": {
   "ik": {
   "type": "text",
   "analyzer": "ik_max_word"
   }
   }
   }
   }
   }
   }
   }

2. create es table.....

3. See error
   

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

[wuyunfeng]

resolved by #4300