[share_plus] mimeTypes parameter of shareFiles method is missing documentation

[Boehrsi]

System info

Issue occurs on: both
Plugin name: share_plus
Plugin version: 3.0.2

Steps to Reproduce

1. Open https://pub.dev/documentation/share_plus/latest/share_plus/Share/shareFiles.html or view the in-code documentation while developing
2. The mimeTypes parameter of the shareFiles method is missing documentation.

More information

Already prepared a hopefully fitting PR.