doc: extensions: kconfig: improve search capabilities

This patch modifies the Kconfig search _algorithm_ so that it aligns
with how menuconfig search works:

- Input is splitted into multiple search terms (space based split)
- Both Kconfig option name and prompt are used
- Regex search is used instead of match, it is less efficient but will
  search the whole string, leading to more results.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

doc/_extensions/zephyr/kconfig/static/kconfig.mjs

@@ -289,11 +289,23 @@ function doSearch() {
     }
 
     /* perform search */
-    let pattern = new RegExp(input.value, 'i');
+    const regexes = input.value.trim().split(/\s+/).map(
+        element => new RegExp(element.toLowerCase())
+    );
     let count = 0;
 
     const searchResults = db.filter(entry => {
-        if (entry.name.match(pattern)) {
+        let matches = 0;
+        const name = entry.name.toLowerCase();
+        const prompt = entry.prompt ? entry.prompt.toLowerCase() : "";
+
+        regexes.forEach(regex => {
+            if (name.search(regex) >= 0 || prompt.search(regex) >= 0) {
+                matches++;
+            }
+        });
+
+        if (matches === regexes.length) {
             count++;
             if (count > searchOffset && count <= (searchOffset + MAX_RESULTS)) {
                 return true;