Fix input configuration implementation

[AlanGriffiths]

Some of this code was written with an incorrect understanding (that multiple click and scroll modes could be active at once).

That required an API change.

Also some improved logging and tidying up.

No test changes, as the functionality isn't actually affected.

[codecov]

Codecov Report

Attention: Patch coverage is 47.13376% with 83 lines in your changes missing coverage. Please review.

Project coverage is 77.27%. Comparing base (bc301b6) to head (0613d64).
Report is 438 commits behind head on main.

Files with missing lines	Patch %	Lines
...demo_server/server_example_input_device_config.cpp	42.85%	44 Missing ⚠️
src/platforms/evdev/libinput_device.cpp	48.43%	33 Missing ⚠️
src/common/input/mir_touchpad_config.cpp	55.55%	4 Missing ⚠️
...r_demo_server/server_example_input_device_config.h	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3407      +/-   ##
==========================================
- Coverage   77.31%   77.27%   -0.05%     
==========================================
  Files        1075     1075              
  Lines       68345    68401      +56     
==========================================
+ Hits        52841    52854      +13     
- Misses      15504    15547      +43     

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[mattkae]

Some nitpicks, but overall looks good

[mattkae]

Looks good to me 👍