Introduce a new `/* HH_TRACE[$var] */` annotation

while analyzing a script, it would be nice to be able to inspect the type of a variable if it's not a parameter.

e.g:
```
$pattern = re"/(?PPHP)/";
```

`$pattern` in this case is `shape(0 => string, 'langauge' => string)`, however, the only way to know this statically, is by using an editor with hack plugin, which would ask hh_client for the information.

## request

This issue requests a new hh_client "annotation" `HH_TYPE`/`HH_TRACE` which will result in an error that contains type information about given variable ( e.g: https://cloud.void.tn/c/36?version=4.114.0 )

This feature is inspired by psalm trace feature: https://psalm.dev/r/1602ca9415

Start by reading the requested hh_client annotation behavior, including the proposed HH_TYPE/HH_TRACE names and the linked type-inspection example. Compare the requested output with Psalm's trace feature, then define the annotation syntax, error contents, and validation needed for a variable such as $pattern.

Written by the indexing model from the issue text.