[Security Solution][Detections] Follow up cleanup after two bugfixes (#87516)

## Summary

This is a follow-up PR addressing some of the comments in:

- https://github.com/elastic/kibana/pull/86908
- https://github.com/elastic/kibana/pull/87004

x-pack/plugins/security_solution/public/common/components/autocomplete/field.tsx

@@ -122,16 +122,16 @@ const getAvailableFields = (
   selectedFields: IFieldType[],
   fieldTypeFilter: string[]
 ): IFieldType[] => {
-  const map = new Map<string, IFieldType>();
+  const fieldsByName = new Map<string, IFieldType>();
 
-  existingFields.forEach((f) => map.set(f.name, f));
-  selectedFields.forEach((f) => map.set(f.name, f));
+  existingFields.forEach((f) => fieldsByName.set(f.name, f));
+  selectedFields.forEach((f) => fieldsByName.set(f.name, f));
 
-  const array = Array.from(map.values());
+  const uniqueFields = Array.from(fieldsByName.values());
 
   if (fieldTypeFilter.length > 0) {
-    return array.filter(({ type }) => fieldTypeFilter.includes(type));
+    return uniqueFields.filter(({ type }) => fieldTypeFilter.includes(type));
   }
 
-  return array;
+  return uniqueFields;
 };

x-pack/plugins/security_solution/public/common/components/links_to_docs/doc_link.tsx

@@ -22,7 +22,11 @@ const DocLink: FC<DocLinkProps> = ({ guidePath = 'security', docPath, linkText }
   const url = `${ELASTIC_WEBSITE_URL}guide/en/${guidePath}/${DOC_LINK_VERSION}/${docPath}`;
   const ariaLabel = `${linkText} - ${COMMON_ARIA_LABEL_ENDING}`;
 
-  return <ExternalLink url={url} text={linkText} ariaLabel={ariaLabel} />;
+  return (
+    <ExternalLink url={url} ariaLabel={ariaLabel}>
+      {linkText}
+    </ExternalLink>
+  );
 };
 
 /**

x-pack/plugins/security_solution/public/common/components/links_to_docs/external_link.tsx

@@ -5,21 +5,34 @@
  */
 
 import React, { FC } from 'react';
-import { EuiLink } from '@elastic/eui';
+import { EuiLink, EuiToolTip } from '@elastic/eui';
 
 interface ExternalLinkProps {
   url: string;
-  text: string;
+  children?: React.ReactNode;
   ariaLabel?: string;
 }
 
 /**
- * A simplistic text link for opening external urls in a new browser tab.
+ * A link for opening external urls in a new browser tab.
  */
-export const ExternalLink: FC<ExternalLinkProps> = ({ url, text, ariaLabel }) => {
+export const ExternalLink: FC<ExternalLinkProps> = ({ url, children, ariaLabel }) => {
+  if (!children) {
+    return null;
+  }
+
   return (
-    <EuiLink href={url} aria-label={ariaLabel} external target="_blank" rel="noopener">
-      {text}
-    </EuiLink>
+    <EuiToolTip content={url} position="top" data-test-subj="externalLinkTooltip">
+      <EuiLink
+        href={url}
+        aria-label={ariaLabel}
+        external
+        target="_blank"
+        rel="noopener"
+        data-test-subj="externalLink"
+      >
+        {children}
+      </EuiLink>
+    </EuiToolTip>
   );
 };