Incorrect colors are used for \xN8 and \xN9 in strings in Rust

[noritada]

Type: Bug

In strings in Rust, \xN8 and \xN9 (N = 0-7) are colored incorrectly.
Although these characters are ASCII, they are colored in the same way as non-ASCII characters.

I have fixed this issue locally and will send a PR later.

Many thanks,

VS Code version: Code 1.73.1 (6261075, 2022-11-09T02:08:38.961Z)
OS version: Darwin x64 19.6.0
Modes:
Sandboxed: No

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-7660U CPU @ 2.50GHz (4 x 2500)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled metal: disabled_off multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_renderer: enabled_on video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: disabled_off
Load (avg)	3, 6, 5
Memory (System)	16.00GB (0.28GB free)
Process Argv	. --crash-reporter-id a4a7ae6c-8e69-447d-8b0d-f4f038ddd3e6
Screen Reader	no
VM	0%

Extensions: none

A/B Experiments

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[alexr00]

We get our Rust syntax highlighting grammar from https://github.com/dustypomerleau/rust-syntax. I've moved the issue to dustypomerleau/rust-syntax#33 and linked your PR.