Add a HINT and a directive to match all CoreLibs apps

[Alex-302]

Problem: We have 4 platforms, based on CoreLibs, and directives

• adguard_app_windows — AdGuard for Windows
• adguard_app_mac — AdGuard for Mac
• adguard_app_cli — AdGuard for Linux
• adguard_app_android — AdGuard for Android

and hints

• windows — AdGuard for Windows
• mac — AdGuard for Mac
• cli — AdGuard for Linux
• android — AdGuard for Android

Now, when solving problems common to all these programs, we need to list all directives or HINTS. The directive is excessively long and difficult to read.

Proposed solution:

Add:

• a directive for all CoreLibs programs
  adguard_app_cl
• a hint for all CoreLibs programs
  apps_cl or something like that.