[build] improve wayland build config

This change reduces the visibility of the internal wayland targets, as
well as changes the wayland.gni templates to implicitly propagate deps
to callers. For example, a target that defines a wayland_protocol_header
target will automatically use the include path for that header.

Test: CQ
Change-Id: Ice1d81a1d307790d233b76594e630602d78b0f3c