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-derive-docs/tests/doc_comment_with_code.gen

@@ -101,15 +101,7 @@ impl crate::docs::StdLibFn for MyFunc {
         let mut settings = schemars::gen::SchemaSettings::openapi3();
         settings.inline_subschemas = inline_subschemas;
         let mut generator = schemars::gen::SchemaGenerator::new(settings);
-        vec![crate::docs::StdLibFnArg {
-            name: "args".to_string(),
-            type_: "kittycad::types::InputFormat".to_string(),
-            schema: generator.root_schema_for::<Option<kittycad::types::InputFormat>>(),
-            required: false,
-            label_required: true,
-            description: String::new().to_string(),
-            include_in_snippet: false,
-        }]
+        vec![]
     }
 
     fn return_value(&self, inline_subschemas: bool) -> Option<crate::docs::StdLibFnArg> {
@@ -125,6 +117,8 @@ impl crate::docs::StdLibFn for MyFunc {
             label_required: true,
             description: String::new(),
             include_in_snippet: true,
+            snippet_value: None,
+            snippet_value_array: None,
         })
     }