Add WebGPU Shading Language (WGSL) filetype (#12723)

Add WebGPU Shading Language (WGSL) filetype (#12723)

The current W3C Working Draft for the WebGPU Shading Language (WGSL) specifies
'text/wgsl' media type for WGSL modules with the '.wgsl' file extension:
https://www.w3.org/TR/WGSL/#text-wgsl-media-type

It has also been registered at the Internet Assigned Numbers Authority (IANA):
https://www.iana.org/assignments/media-types/text/wgsl

Neovim's nvim-lspconfig already associates wgsl language servers
with 'filetype wgsl':
https://github.com/neovim/nvim-lspconfig/blob/master/doc/server_configurations.md#wgsl_analyzer

However currenly setting 'filetype wgsl' for *.wgsl files by defalut in Neovim
is blocked by adding this filetype to the vim project first:
https://github.com/neovim/neovim/pull/23331

This commit adds this missing wgsl filetype.