gdbus: rename doc/*-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/assisted-satellite-navigation-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/audio-settings-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/call-barring-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/call-forwarding-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/cdma-connman-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/modem-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
gdbus: convert doc/voicecallmanager-api.txt

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>