Theia does not accept .../latest/file/download as plugin URL

[goekce]

Bug Description:

If I use the URL for the latest version of a plugin like:

"theiaPlugins": {                                                                                                                                                                                                                    
       "vscode-builtin-extensions-pack": "https://open-vsx.org/api/eclipse-theia/builtin-extension-pack/latest/file/download"                                                                                                           },

Then I get the following error:

... has an unsupported file type: ...

Related lines:

theia/dev-packages/cli/src/download-plugins.ts

Lines 206 to 215 in c32cbda

	if (pluginUrl.endsWith('tar.gz')) {
	fileExt = '.tar.gz';
	} else if (pluginUrl.endsWith('vsix')) {
	fileExt = '.vsix';
	} else if (pluginUrl.endsWith('theia')) {
	fileExt = '.theia'; // theia plugins.
	} else {
	failures.push(chalk.red(`error: '${plugin}' has an unsupported file type: '${pluginUrl}'`));
	return;
	}

Related: eclipse/openvsx#507

Steps to Reproduce:

1. Add above plugin link to package.json
2. yarn theia download:plugins

Additional Information

• Operating System: Arch Linux
• Theia Version: 1.42 (latest)