Use bool directly in InputMessage

In order to send the data via socket, we use the InputMessage struct. In
this struct, various fields are stored. This struct's purpose is to
serialize the input event information.

We are storing bools in InputMessage as various integer types. To read
these bools, we compare the integers to 1. It's not very convenient.

To simplify this, let's store bools directly in InputMessage. Bool size
is implementation-dependent, but it's typically 1, so we can just guard
against that with a static_assert.

Bug: 169866723
Test: presubmit
Change-Id: Iae4870fac95e884cc328791c0035df6e31e34a7b