Some effects delete Envelope Control Points, or do not move them when timeline changes

[crsib]

Describe the bug

Effect using ClearAndPaste, as well as Equalization (which is not) do not preserve Envelope points. This issue is reintroduced after reverting:

• 58adb94
• c13a074

However, it is considered to have much lower priority

To Reproduce
Steps to reproduce the behavior:

1. Create an envelope.
2. Use ONE of these effects:

a. Change Speed/Pitch/Tempo
b. An EQ effect (see bug 1686)
c. Noise Removal
d. Nyquist Prompt
e. Sliding Time Scale/Pitch Shift
f. Copy-paste

Envelope points are deleted.

Expected behavior
Envelope points should not be deleted. Discontinuities should not be added for effects, only when copying

[Paul-Licameli]

Actually, rather than reversion, what happens if the calls to Envelope::Insert() are instead made to Envelope::InsertOrReplace()? I think this will preserve the bug fix, and also not corrupt the envelope because points will remain properly sorted.

[crsib]

The behavior will be still buggy because Clear introduces discontinuities, that are totally not expected when applying the effect. I believe that (10 years) old buggy behavior is preferred to new buggy behavior, with the consequences not known so well.

Also, the new behavior will still introduce 4 new points for each effect usage.

[Paul-Licameli]

How four, not two? You mean, in a stereo track, not mono.

[crsib]

How four, not two? You mean, in a stereo track, not mono.

Sure, two, you are right

[Paul-Licameli]

Of course we mean two discontinuities, four points.