Can the tree-sitter/build-module/build.sh support Mingw64 on Windows OS

[Eason Huang]

Hi emacs-devel team,

Recently the script from admin/notes/tree-sitter/build-module/build.sh
only support macOS and Linux. It would be nice to support Windows system
as well.

I can confirm that we only need to use soext="dll" and it will work well
on mingw64 of msys2.

The $(uname) will return "MINGW64_NT-10.0-22000" on the mingw64.

But I am not sure how to adapt the below code to support mingw64.

from line 6 of build.sh:
```
if [ $(uname) == "Darwin" ]
then
    soext="dylib"
else
    soext="so"
fi
```

-- 
Eason Huang