Add strings for developer settings link to WebView DevTools UI

This specific change adds string definitions for a WebView DevTools UI
entry point in Android developer settings.

Bug: 371520781
Test: atest SettingsRoboTests:com.android.settings.development.WebViewDevUiPreferenceControllerTest
Flag: EXEMPT new entry point to a feature which already exists
Change-Id: I0c2d37e658dc111b0e5255becbac1fe8d424935c