fix identifierLocFromIndex on escaped identifier

[Techatrix]

fixes #2023

[Sekky61]

Works well for me. It also closes #2035.
I just found a small annoyance, see this test:

    try testHover(
        \\const @<cursor>"hello  world" = 42;
    ,
        \\```zig
        \\const @"hello  world" = 42
        \\```
        \\```zig
        \\(comptime_int)
        \\```
    );

It does not work on the left quote, but it does again work at the @.

[Techatrix]

I just found a small annoyance, see this test:

This is caused in a different part of the codebase (position_context). Coincidentally I have worked on a refactor of that component which appears to fix this case. I will publish that in a separate PR.