C++20: consteval and constinit keywords

[jgcodes2020]

Checklist

• [x] This problem exists even with the setting "C_Cpp.enhancedColorization": "Disabled"

The code with a problem is:

consteval void test_1() {
}
constinit int test_2 {2};

It looks like:

this, with One Dark Pro

It should look like:

consteval and constinit should be marked as keywords, as GitHub does with the above section.

[jgcodes2020]

Closing, as this is just a part of #396.