Support for c++ string literals syntax higlighting

[dortamiguel]

It's pretty useful to use string literals in c++ string literals like this

const char* shader_code = R"(
    #version 460 core

    out vec4 FragColor;

    in vec4 color;

    void main(void) {
      FragColor = color;
    }
)";

Could be possible to support syntax higlighting in string literals with c++?

[hsimpson]

At the moment this extension is not responsible for syntax highlighting only for linting of shader code. The highlighting support comes from a dependent extension, which I will remove in the future see #25

But C++ string literals are not yet supported for linting. I will be possible to implement via configurable regular expressions.