API4 user-facing backward incompatible changes

[AkarinVS]

We should definitely fix all these issues as they impact real scripts:

• removed get_read_array and get_write_array, see PR cython: restore old low-level frame data access APIs (take 2) vapoursynth/vapoursynth#744 and cython: restore old low-level frame data access APIs vapoursynth/vapoursynth#738 (I won't allow introducing of numpy dependency though.)
• removed bint delete support from std.SetFrameProp, see PR std: restore ability to delete frame property with SetFrameProp vapoursynth/vapoursynth#739
• VideoOutputTuple replaced AlphaOutputTuple breaking vsp: vapoursynth@ef7a731
• vs.Format changed to vs.VideoFormat, add an alias.
• core.get_plugins() deprecated. Reverse the deprecation.
• vs.register_format deprecated. Reverse the deprecation.
• removed vs.get_core() and other deprecated functions. Add them back.
  • vs.get_core(add_cache=False) support (used by seek-test.py)
• core.add_cache removed. Just add a dummy property.
• vspipe no longer changes the current directory into the script's directory, that is, -c is now always active, breaking a feature dated back to R46. What's more, now -c is an entirely different feature (--container). R56 further complicates this by reverting to the previous behavior without having a way to disable it (as vspipe -c is reused to mean something entire different)
• vspipe -a will pass as str, not bytes objects. // introduce vspipe3 that restores R54 behavior? (A universal workaround: when passing utf-8 strings, use a = os.fsdecode(a) to get a string no matter the type of a is str or bytes.(os.fsdecode does not work on Windows as it doesn't always use utf-8 encoding.) If only passing filenames to source filters, then the type of variables doesn't matter.)
• api3 filters that return alpha clips are broken (the alpha clip is never requested)
• (R57) leading underscore in filter parameter names are no longer skipped (to fix std.SetFrameProps). VS-C will strip the leading underscore only for std.SetFrameProps alone to retain compatibility with older VS versions.
• api3 python VideoFrame has a planes() undocumented API, which is used by VapourSynth-TCPClip.
• resize plugins switched the default value for option prefer_props from False (R54) to True(R58) and trigger a warning. (vs-c will keep prefer_props=False default of R54). R58 also silently removed the option. After facing backlashes from previewers, added back the option but totally ignored its setting.

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Possibly unfixable?

1. vs.YCOCG color space
2. modified preset format numbers?
3. vnode vs node in function parameters.

[AkarinVS]

Release R55.A2b status snapshot:

We should definitely fix all these issues as they impact real scripts:

• removed get_read_array and get_write_array, see PR cython: restore old low-level frame data access APIs (take 2) vapoursynth/vapoursynth#744 and cython: restore old low-level frame data access APIs vapoursynth/vapoursynth#738 (I won't allow introducing of numpy dependency though.)
• removed bint delete support from std.SetFrameProp, see PR std: restore ability to delete frame property with SetFrameProp vapoursynth/vapoursynth#739
• VideoOutputTuple replaced AlphaOutputTuple breaking vsp: vapoursynth@ef7a731
• core.get_plugins() deprecated. Reverse the deprecation.
• vs.register_format deprecated. Reverse the deprecation.
• removed vs.get_core() and other deprecated functions. Add them back.
  • vs.get_core(add_cache=False) support (used by seek-test.py)
• core.add_cache removed. Just add a dummy property.
• vspipe no longer changes the current directory into the script's directory, that is, -c is now always active. What's more, now -c is an entirely different feature (--container).
• vspipe -a will pass as str, not bytes objects. // introduce vspipe3 that restores R54 behavior?
• api3 filters that return alpha clips are broken (the alpha clip is never requested)