Add 'explicit' to Android embedder constructors

[jmagman]

Add explicit to constructor declarations in android_debug.

Include headers using header filter regex:

Checks: '-*,google-explicit-constructor'
WarningsAsErrors: '-*,google-explicit-constructor'
HeaderFilterRegex: '.*/flutter/.*h$'

https://clang.llvm.org/extra/clang-tidy/checks/google-explicit-constructor.html

Android version of #29741
For flutter/flutter#93576

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat.

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[jmagman]

Once the Android warning is fixed I will turn on the android_debug linter in the recipe:
https://ci.chromium.org/raw/build/logs.chromium.org/flutter/led/magder_google.com/a607d51368817f8141be366e4a2e08f563fc08ba866a6241b2d0890c2292a8e0/+/build.proto?server=chromium-swarm.appspot.com

https://flutter-review.googlesource.com/c/recipes/+/22160

[jmagman]

Tree is actually green, the status isn't updating. Merging.

[zanderso]

lgtm