* intern_pool: add getUnsignedInt
* add an empty struct literal
* resolve array length as usize in comptime interpreter
* use only one global intern pool
* store analysis errors in `DocumentStore.Handle`
* add typed undefined value
* add typed null value
As reported on Discord by CodotakuYT:
```zig
fn populate(T: type, index: i32) T {
_ = index;
@typeInfo(T).struct.
}
```
```
thread 17384 panic: access of union field 'ast_node' while field 'param_payload' is active
C:\Users\taoua\zls\src\features\completions.zig:875:61: 0x7ff68070caac in completeDot (zls.exe.obj)
const node_data = nodes_data[local_decl.decl.ast_node];
```
* move language feature files into separate folder
* move code completions into features/completions.zig
* move goto definition/declaration into features folder
* move hover into features folder
* restructure imports
* move selection range into features folder
* restructure request handling tracy call
* add missing features to `zls.zig`
