Use new libsidplay API for SID plugin

[radioactiveman]

Description
libsidplay 2.14 introduced a new play API. The play() function we use was deprecated, leading to this warning:

[1/2] Compiling C++ object src/sid/sid.so.p/xs_sidplay2.cc.o
../src/sid/xs_sidplay2.cc: In function ‘unsigned int xs_sidplayfp_fillbuffer(char*, unsigned int)’:
../src/sid/xs_sidplay2.cc:223:31: warning: ‘uint_least32_t sidplayfp::play(short int*, uint_least32_t)’ is deprecated [-Wdeprecated-declarations]
  223 |     return state.currEng->play((short *)audioBuffer, audioBufSize / 2) * 2;
      |            ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../src/sid/xs_sidplay2.cc:33:
/usr/include/sidplayfp/sidplayfp.h:115:20: note: declared here
  115 |     uint_least32_t play(short *buffer, uint_least32_t count);
      |                    ^~~~

Since I don't understand how to migrate our SID plugin to the new API, I file it here as feature request.
@jlindgren90: Maybe you want to take care of it?

Additional information

• Updated demo: libsidplayfp/libsidplayfp@eec529e
• Removal of the old API for libsidplay 3.0 (not released yet): libsidplayfp/libsidplayfp@016c871

[mschwendt]

Exposing a low-level "cycles" parameter to the library API users is odd IMO. The internal clock speed is around 1 MHz, but a simple way to fill a buffer with output samples would be convenient.

After a quick glance at the related changes, it seems the combination of play() and mix() would work:
libsidplayfp/libsidplayfp@e7787cb