Implement include path annotation.

Include top annotation is a specially formatted comment line providing
the include/inhherit file location hint. E.g., adding
```
```
before
```
$(call inherit-product $(SRC)/foo.mk
```
is a hint to the converter to look for the `foo.mk` files under
`vendor/my_vendor/` in addition to `vendor/google_devices/'

Bug: 193566316
Test: internal
Change-Id: I01c5dde2504f1a9eb724098b1cc03d2176ca2cf9