R55.A0 Initial test release

[AkarinVS]

Integrated python 3.9.6 embeddable and vsedit https://github.com/YomikoR/VapourSynth-Editor/releases/tag/r19-mod-2.
Due to the use of mimalloc, vspipe might crash on non-Windows 10/11 systems. Though vsedit works on those systems.

Remaining incompatibilities:

• alpha clips from source filters are ignored for api3 source filters (known bug API4 user-facing backward incompatible changes #2)
• vspipe follows api4 behavior, see API4 user-facing backward incompatible changes #2 for details
• need to use latest fmtconv release due to different predefined format constants.
• vs.YCOCG and vs.COMPATBGR32 are removed
• builtin filter uses vnode instead of node for their parameter values, however, this is out of the scope for this fork as we aim for vpy level compatibility.

Missing plugins:

• subtext
• imwri
• ocr

Please report any incompatibility with your R54/R55 vpy scripts.

(For AmusementClub members, the latest filter pack should work well.)

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This discussion was created from the release R55.A0 Initial test release.