Decouple AdsServiceImpl full screen mode business logic

[tmancey]

No description provided.

[stephendonner]

Verified PASSED using the testplan from brave/brave-core#8265 on build

Brave	1.24.47 Chromium: 90.0.4430.41 (Official Build) nightly (x86_64)
Revision	e9c92b1eaca8487e212f3f6bc081fdb6d4863759-refs/branch-heads/4430@{#723}
OS	macOS Version 11.2.3 (Build 20D91)

Steps:

1. launched Brave nightly on a clean profile, using --enable-logging=stderr --vmodule="*/bat-native-ledger/*"=6,"*/brave_rewards/*"=6,"*/bat-native-ads/*"=6,"*/bat-native-confirmations/*"=6,"*/brave_ads/*"=9,"*/brave_user_model/*"=6 --brave-ads-staging --brave-ads-debug --rewards=staging=true
2. opened a few tabs
3. clicked on View -> Enter Full Screen
4. waited
5. interacted with the page in full-screen mode

Confirmed no ads were displayed

Logs:

[752:775:0405/152641.029038:VERBOSE2:epsilon_greedy_bandit_resource.cc(62)]   untargeted
[752:775:0405/152720.919102:VERBOSE1:subdivision_targeting.cc(164)] Fetch subdivision target
[752:775:0405/152720.919296:VERBOSE2:subdivision_targeting.cc(165)] GET /v1/getstate
[752:775:0405/152720.919391:VERBOSE5:subdivision_targeting.cc(169)] URL Request:
  URL: https://ads-serve.bravesoftware.com/v1/getstate
  Method: BraveAdsUrlRequestMethod::GET
[752:775:0405/152720.932944:VERBOSE6:subdivision_targeting.cc(178)] URL Response:
  URL: https://ads-serve.bravesoftware.com/v1/getstate
  Response Status Code: 200
  Response: {"country":"US", "region":"CA"}
[752:775:0405/152720.933048:VERBOSE1:subdivision_targeting.cc(184)] Successfully fetched subdivision target
[752:775:0405/152720.933485:VERBOSE1:subdivision_targeting.cc(205)] Automatically detected subdivision targeting code as US-CA
[752:775:0405/152720.934293:VERBOSE1:subdivision_targeting.cc(262)] Fetch ads subdivision target in 0 hours, 2 minutes, 37 seconds at 3:29 PM
[752:775:0405/152839.515958:VERBOSE1:ads_impl.cc(202)] Browser state changed to unidle after 3 s
[752:775:0405/152839.519197:VERBOSE2:permission_rule_util.cc(23)] Browser window is not active
[752:775:0405/152839.519274:VERBOSE1:ad_notification_serving.cc(150)] Ad notification not served: Not allowed
[752:775:0405/152839.519323:VERBOSE1:ad_notification_serving.cc(91)] Ad notification not delivered

Example	Example