Effects in wrong menu if type is changed

[petersampsonaudacity]

Describe the bug
If the "type" of a plug-in that has already been registered is changed, the plug-in does not move to the correct menu for the new type.

The problem appears to be that the menus are populated from the pluginregistry.cfg file, which does not get updated when plug-ins change.

Originally logged on Bugzilla as P3 1942

To Reproduce
Steps to reproduce the behavior:

1. Open an installed plug-in in a plain text editor,
2. Find the line near the top that starts with:
   $type

The type will be one of:
process
analyze
generate
tool
tool .... (one of the first three types).

3. Change the type to one that belongs in a different menu. For example if it is a "process" (Effect menu) type, change it to a "generate" type.
   eg. from:
   $type process
   to:
   $type generate

4. Observe: the plug-in does not move to the new menu.

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
If applicable, add screenshots to help explain your problem.

Additional information (please complete the following information):

• OS: [e.g. Mac High Sierra, Ubuntu 18.04, Windows 10]
• Version [e.g. Audacity 2.5.1]
• (if relevant) Sound Device [e.g. Windows WASAPI, USB Sound card]

Additional context
To get the plug-in to appear in the new menu after the type has been changed, it is necessary to:

1. Close Audacity
2. Delete pluginregistry.cfg
3. Restart Audacity.

We have had reports from very confused users about "Sample Data Export" being in the wrong menu (which I believe is due to this bug).