Chrome 138 adds CSS sibling-count() and sibling-index() (#27019)

* Add sibling-count() and sibling-index()

The data was collected from Chrome 137 (stable) and 138 (beta) using new
tests in the collector:
openwebdocs/mdn-bcd-collector#2453

These will be a single feature in web-features, so the same tag is used.

* Update sibling-count.json

* Update sibling-index.json

* Update sibling-count.json

* Update sibling-index.json

* Apply suggestions from code review

Co-authored-by: Claas Augner <495429+caugner@users.noreply.github.com>

---------

Co-authored-by: Claas Augner <495429+caugner@users.noreply.github.com>

Author: foolip

css/types/sibling-count.json

@@ -0,0 +1,42 @@
+{
+  "css": {
+    "types": {
+      "sibling-count": {
+        "__compat": {
+          "description": "`sibling-count()`",
+          "spec_url": "https://drafts.csswg.org/css-values-5/#funcdef-sibling-count",
+          "support": {
+            "chrome": {
+              "version_added": "138"
+            },
+            "chrome_android": "mirror",
+            "edge": "mirror",
+            "firefox": {
+              "version_added": false,
+              "impl_url": "https://bugzil.la/1953973"
+            },
+            "firefox_android": "mirror",
+            "ie": {
+              "version_added": false
+            },
+            "oculus": "mirror",
+            "opera": "mirror",
+            "opera_android": "mirror",
+            "safari": {
+              "version_added": false
+            },
+            "safari_ios": "mirror",
+            "samsunginternet_android": "mirror",
+            "webview_android": "mirror",
+            "webview_ios": "mirror"
+          },
+          "status": {
+            "experimental": true,
+            "standard_track": true,
+            "deprecated": false
+          }
+        }
+      }
+    }
+  }
+}

css/types/sibling-index.json

@@ -0,0 +1,42 @@
+{
+  "css": {
+    "types": {
+      "sibling-index": {
+        "__compat": {
+          "description": "`sibling-index()`",
+          "spec_url": "https://drafts.csswg.org/css-values-5/#funcdef-sibling-index",
+          "support": {
+            "chrome": {
+              "version_added": "138"
+            },
+            "chrome_android": "mirror",
+            "edge": "mirror",
+            "firefox": {
+              "version_added": false,
+              "impl_url": "https://bugzil.la/1953973"
+            },
+            "firefox_android": "mirror",
+            "ie": {
+              "version_added": false
+            },
+            "oculus": "mirror",
+            "opera": "mirror",
+            "opera_android": "mirror",
+            "safari": {
+              "version_added": false
+            },
+            "safari_ios": "mirror",
+            "samsunginternet_android": "mirror",
+            "webview_android": "mirror",
+            "webview_ios": "mirror"
+          },
+          "status": {
+            "experimental": true,
+            "standard_track": true,
+            "deprecated": false
+          }
+        }
+      }
+    }
+  }
+}