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/docs/mod.rs

@@ -111,6 +111,13 @@ pub struct StdLibFnArg {
     /// Include this in completion snippets?
     #[serde(default, skip_serializing_if = "is_false")]
     pub include_in_snippet: bool,
+    /// Snippet should suggest this value for the argument.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub snippet_value: Option<String>,
+    /// Snippet should suggest this value for the argument.
+    /// The suggested value should be an array, with these elements.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub snippet_value_array: Option<Vec<String>>,
     /// Additional information that could be used instead of the type's description.
     /// This is helpful if the type is really basic, like "u32" -- that won't tell the user much about
     /// how this argument is meant to be used.
@@ -165,6 +172,21 @@ impl StdLibFnArg {
         } else {
             ""
         };
+        if let Some(vals) = &self.snippet_value_array {
+            let mut snippet = label.to_owned();
+            snippet.push('[');
+            for (i, val) in vals.iter().enumerate() {
+                snippet.push_str(&format!("${{{}:{}}}", index + i, val));
+                if i != vals.len() - 1 {
+                    snippet.push_str(", ");
+                }
+            }
+            snippet.push(']');
+            return Ok(Some((index + vals.len(), snippet)));
+        }
+        if let Some(val) = &self.snippet_value {
+            return Ok(Some((index, format!("{label}${{{}:{}}}", index, val))));
+        }
         if (self.type_ == "Sketch"
             || self.type_ == "[Sketch]"
             || self.type_ == "Geometry"
@@ -988,6 +1010,13 @@ mod tests {
         assert_eq!(snippet, r#"startSketchOn(${0:XY})"#);
     }
 
+    #[test]
+    fn get_autocomplete_snippet_start_profile() {
+        let start_sketch_on_fn: Box<dyn StdLibFn> = Box::new(crate::std::sketch::StartProfile);
+        let snippet = start_sketch_on_fn.to_autocomplete_snippet().unwrap();
+        assert_eq!(snippet, r#"startProfile(${0:%}, at = [${1:0}, ${2:0}])"#);
+    }
+
     #[test]
     fn get_autocomplete_snippet_pattern_circular_3d() {
         // We test this one specifically because it has ints and floats and strings.