inputflinger: Add support for scaling and true value reporting

-1/+1 somewhat simplifies the values that can be generated by rotary
encoders, and rules out the possibility of batching and more nuanced
movement reporting.

So, we modify the device configuration to allow values other than -1 and
1 to be supported. In order to give the developer a sense of what these
values map to in terms of angular displacement, we also parse a
resolution configuration from the devices IDC file.

This will be specified as:

device.res = xxxx

of type float. If a value is not provided, a default res value of 0.0f
is used.

This patch also adds a per device scaling factor, which is used to
suitably modify the values reported (as well as the resolution) to tune
the input events generated and resulting UI according to the hardware.
This can be specified in the IDC file as:

device.scalingFactor = xxxx

of type float. If a scaling factor is not provided, a default of 1.0f
is used.

Bug: 22836852
Bug: 18707397
Change-Id: I13686f64de1b52d3f6c97b2587ae41e52d1db6e2