Clean up frontend file upload code

[leblowl]

With #2306 it looks like we might be able to remove this logic:

quiet/packages/desktop/src/renderer/components/Channel/Channel.tsx

Lines 124 to 128 in 9693d0d

	if (name === 'image') {
	id = `${Date.now()}_${Math.random().toString(36).substring(0, 20)}`
	} else {
	id = name
	}

or at least move it all into the writeTempFile handler so the logic is altogether.

Other ideas:

• Move some of this logic out of the component and into handleClipboardFiles:

  quiet/packages/desktop/src/renderer/components/widgets/channels/ChannelInput/ChannelInput.tsx

  Lines 375 to 378 in 21aa761

  	const fileExt = path.extname(files[i].name).toLowerCase()
  	const fileName = path.basename(files[i].name, fileExt)
  	const arrayBuffer = await files[i].arrayBuffer()
  	handleClipboardFiles(arrayBuffer, fileExt, fileName)

• Unify the two methods for selecting a file to upload (copy/paste and file manager):

  quiet/packages/common/src/fileData.ts

  Lines 4 to 13 in 21aa761

  	export const getFileData = (filePath: string, isTmpPath = false): FilePreviewData => {
  	const fileContent: FileContent = {
  	path: filePath,
  	tmpPath: isTmpPath ? filePath : undefined,
  	name: path.basename(filePath, path.extname(filePath)),
  	ext: path.extname(filePath).toLowerCase(),
  	}
  	const id = `${Date.now()}_${Math.random().toString(36).substring(0, 20)}`
  	return { [id]: fileContent }
  	}

I haven't looked too deeply at this code, so you might want to check my assumptions before making changes. But in general it looks like we can clean things up a bit. Feel free to get creative with it.