Add dependencies on absl when they are used but undeclared

Bug: b/36882554
Change-Id: I3a1c5f0024abc452bcd74eef2b66d4493f4f974c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/266760
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37320}

modules/video_coding/codecs/av1/BUILD.gn

@@ -89,6 +89,7 @@ rtc_library("libaom_av1_encoder") {
   ]
   absl_deps = [
     "//third_party/abseil-cpp/absl/algorithm:container",
+    "//third_party/abseil-cpp/absl/base:core_headers",
     "//third_party/abseil-cpp/absl/strings:strings",
     "//third_party/abseil-cpp/absl/types:optional",
   ]