src/vs/platform/environment/common/environmentService.ts/AbstractNativeEnvironmentService/extensionsPath
class AbstractNativeEnvironmentService:	get extensionsPath(): string {
		const cliExtensionsDir = this.args['extensions-dir'];
		if (cliExtensionsDir) {
			return resolve(cliExtensionsDir);
		}

		const vscodeExtensions = env['VSCODE_EXTENSIONS'];
		if (vscodeExtensions) {
			return vscodeExtensions;
		}

		const vscodePortable = env['VSCODE_PORTABLE'];
		if (vscodePortable) {
			return join(vscodePortable, 'extensions');
		}

		return joinPath(this.userHome, this.productService.dataFolderName, 'extensions').fsPath;
	}