Add "aidl.flags:" property for cc_/java_ modules

The property can be used to pass additional flags to the AIDL compiler.
For example,

  cc_library {
    ..
    srcs: ["Foo.aidl"],
    aidl: {
      flags: [
        "-Werror",      // warnings as error
        "-Weverything", // turn on all warnings
      ],
    },
  }

Bug: 168028537
Test: soong test
Change-Id: I8120eeae7cd7b1acdd34c554af996a29e760a368