Add external project webview_support_interfaces.

The project webview_support_interfaces contains a set of interfaces
shared between the WebView Support Library and the WebView APK.

Bug: 73296841
Merged-In: Ife087ebd5cc3895b1365af2cdb42c43320cf885d

default.xml

@@ -387,6 +387,7 @@
   <project path="external/walt" name="platform/external/walt" groups="pdk" />
   <project path="external/webp" name="platform/external/webp" groups="pdk,qcom_msm8x26" />
   <project path="external/webrtc" name="platform/external/webrtc" groups="pdk" />
+  <project path="external/webview_support_interfaces" name="platform/external/webview_support_interfaces" groups="pdk" />
   <project path="external/wpa_supplicant_8" name="platform/external/wpa_supplicant_8" groups="pdk" />
   <project path="external/wycheproof" name="platform/external/wycheproof" groups="pdk" />
   <project path="external/x264" name="platform/external/x264" groups="pdk" />