Don't rely on relative path for docs preprocessor (#16883)

Reapplies #16700 with a corrected command. Now it no longer relies on a
relative path.

Thanks @maxdeviant for the quick help 🙏 

Release Notes:

- N/A

crates/docs_preprocessor/src/templates/keybinding.rs

@@ -0,0 +1,36 @@
+use crate::PreprocessorContext;
+use regex::Regex;
+use std::collections::HashMap;
+
+use super::Template;
+
+pub struct KeybindingTemplate;
+
+impl KeybindingTemplate {
+    pub fn new() -> Self {
+        KeybindingTemplate
+    }
+}
+
+impl Template for KeybindingTemplate {
+    fn key(&self) -> &'static str {
+        "kb"
+    }
+
+    fn regex(&self) -> Regex {
+        Regex::new(&format!(r"\{{#{}(.*?)\}}", self.key())).unwrap()
+    }
+
+    fn parse_args(&self, args: &str) -> HashMap<String, String> {
+        let mut map = HashMap::new();
+        map.insert("action".to_string(), args.trim().to_string());
+        map
+    }
+
+    fn render(&self, context: &PreprocessorContext, args: &HashMap<String, String>) -> String {
+        let action = args.get("action").map(String::as_str).unwrap_or("");
+        let macos_binding = context.find_binding("macos", action).unwrap_or_default();
+        let linux_binding = context.find_binding("linux", action).unwrap_or_default();
+        format!("<kbd class=\"keybinding\">{macos_binding}|{linux_binding}</kbd>")
+    }
+}