feat(ui): Extract StreamMediaAttachmentBuilder widget

[Mounix99]

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Changes requested in issue

CLA

• [x] I have signed the Stream CLA (required).
• [x] The code changes follow best practices
• [x] Code changes are tested (add some information if not applicable)

Description of the pull request

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 59.18%. Comparing base (461986b) to head (dc201b4).

:exclamation: Current head dc201b4 differs from pull request most recent head 120f024

Please upload reports for the commit 120f024 to get more accurate results.

Files	Patch %	Lines
...ge_input/stream_message_input_attachment_list.dart	91.66%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1816      +/-   ##
==========================================
- Coverage   60.27%   59.18%   -1.09%     
==========================================
  Files         317      310       -7     
  Lines       18473    17809     -664     
==========================================
- Hits        11134    10540     -594     
+ Misses       7339     7269      -70     

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[Mounix99]

@kanat can you please review it again ?

[Mounix99]

Review and everything else takes too long, If someone from package developers can manage this PR by themselves, please do it! Thank you, in advance!