Sourcekit-lsp iOS support

clientMain.js

    function sourcekitLspServerOptions() {
        // Load the path to the language server from settings
        const executableCommand = vscode_1.workspace.getConfiguration("sourcekit-lsp").get("serverPath") ||
            vscode_1.workspace
                .getConfiguration("swift")
                .get("languageServerPath", "/usr/local/bin/sourcekit-lsp");
        const toolchain = vscode_1.workspace
            .getConfiguration("sourcekit-lsp")
            .get("toolchainPath");

        const iosSdk = "/Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk";
        const iosTarget = "x86_64-apple-ios13.2-simulator";
        let iosFlags = [];

        if (iosSdk) {
            iosFlags = iosFlags.concat(['-Xswiftc', '-sdk', '-Xswiftc', iosSdk]);
        }

        if (iosTarget) {
            iosFlags = iosFlags.concat(['-Xswiftc', '-target', '-Xswiftc', iosTarget]);
        }

        const env = toolchain
            ? Object.assign(Object.assign({}, process.env), { SOURCEKIT_TOOLCHAIN_PATH: toolchain }) : process.env;
        const run = { command: executableCommand, options: env, args: iosFlags };
        const serverOptions = run;
        return serverOptions;
    }