KCL: Customizable per-arg and per-fn snippet values (#7156)

Before, the LSP snippet for `startProfile` was 

```
startProfile(%, at = [3.14, 3.14])
```

Now it's 

```
startProfile(%, at = [0, 0])
```

This is configured by adding a `snippet_value=` field to the stdlib macro. For example:


```diff
#[stdlib {
    name = "startProfile",
    keywords = true,
    unlabeled_first = true,
    args = {
        sketch_surface = { docs = "What to start the profile on" },
-       at = { docs = "Where to start the profile. An absolute point." },
+       at = { docs = "Where to start the profile. An absolute point.", snippet_value = "[0, 0]" },        tag = { docs = "Tag this first starting point" },
    },
    tags = ["sketch"]
}]
```

## Work for follow-up PRs

 - Make this work for KCL functions defined in KCL, e.g. [`fn circle`](36c8ad439d/rust/kcl-lib/std/sketch.kcl (L31-L32)) -- something like `@(snippet_value = "[0, 0]")` perhaps
 - Go through the stdlib and change defaults where appropriate

rust/kcl-lib/src/std/sketch.rs

@@ -1322,7 +1322,7 @@ pub async fn start_profile(exec_state: &mut ExecState, args: Args) -> Result<Kcl
     unlabeled_first = true,
     args = {
         sketch_surface = { docs = "What to start the profile on" },
-        at = { docs = "Where to start the profile. An absolute point." },
+        at = { docs = "Where to start the profile. An absolute point.", snippet_value_array = ["0", "0"] },
         tag = { docs = "Tag this first starting point" },
     },
     tags = ["sketch"]