Syntax Highlighting optional class variable in type definition file.

[nickzelei]

Issue Type: Bug

VSCode syntax highlighting breaks when it encounters an optional class level variable in a type definition (.d.ts) file.

The example below is a simplified version of what I was seeing in one of my emitted type definition files.

When pasting this block into a .d.ts file, you should see the variables "private readonly" below where test2?; is declared in the TestClient turn from the expected dark blue to a light blue, or the same color as the variable name. This has reaching affects throughout the file and causes other things below it to be improperly rendered. I've provided the TestClient2 definition to show a simple case of it.

// test.d.ts
export declare class TestClient {
    private readonly test1;
    private readonly test2?;
    private readonly test3;
    private readonly test4;
}

export declare class TestClient2 {
    private readonly test1;
    private readonly test2;
    private readonly test3;
    private readonly test4;
    private readonly test5;
}

VS Code version: Code 1.25.1 (1dfc5e5, 2018-07-11T15:43:53.668Z)
OS version: Windows_NT x64 10.0.16299

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz (8 x 3592)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: unavailable_software video_decode: enabled video_encode: enabled vpx_decode: enabled webgl: enabled webgl2: enabled
Memory (System)	15.94GB (8.78GB free)
Process Argv	C:\Program Files\Microsoft VS Code\Code.exe
Screen Reader	no
VM	0%

Extensions (3)

Extension	Author (truncated)	Version
tslint	eg2	1.0.34
vsliveshare	ms-	0.3.504
vscode-icons	rob	7.24.0

[mjbvz]

Opened microsoft/TypeScript-TmLanguage#642 and microsoft/TypeScript-TmLanguage#643 to track this upstream