patch 9.1.1787: filetype: not all Sway config files are recognized

patch 9.1.1787: filetype: not all Sway config files are recognized

Problem:  filetype: not all Sway config files are recognized
Solution: Detect files within */sway/config.d/* as swayconfig filetype
          (Felix Pehla).

Sways default config automatically includes files placed in
@sysconfdir@/sway/config.d/* (see config.in), so it makes sense to use
the sway syntax for those.

related: #18293

Signed-off-by: Felix Pehla <29adc1fd92@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>