bring trimming clips and looping functions form Audacity 3.1

[Reaper10]

Guidelines

• [X] I have read the guidelines.

Is your feature request related to a problem? Please describe.

Could you bring trimming clips functions form Audacity 3.1
https://youtu.be/HpA138b-J9s?t=69

Describe the solution you'd like

Could you bring trimming clips and looping function

Describe alternatives you've considered

none

Additional context

this will help in making tenacity nondestructive The looping functions will help in #713 and #281 For the trim function I've made custom mouse cursors trim out trim in trim cursors.zip

This issue is not a duplicate

• [X] I have confirmed this issue isn't a duplicate.

[n0toose]

Should be done after https://github.com/tenacityteam/tenacity/pull/656 and after importing subsequent/relevant changes.