Test: terminal find / display all matches

[meganrogge]

Refs: #134790

• macOS @sandy081
• linux @gregvanl
• windows @Tyriar

Complexity: 3

Authors: @meganrogge

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We want to align the terminal find experience with that of the editor, so this iteration, made use of the new Xterm registerDecoration API to do so.

Verify that the find experience in the terminal:

• feels nice
• looks good
• behaves similarly to the editor
• shows scrollbar annotations in the right places and an indicator for the currently selected term that updates with findNext and findPrevious
• try setting workbench.colorCustomizations.editor.findMatchBackground and workbench.colorCustomizations.editor.findMatchHighlightBackground to custom colors. These should work on the next search
• try searching for something then adding lines to the buffer - the search results should be updated
• scrolling shouldn't impact anything
• closing the find widget (that still has input) should remove the decorations
• clearing the find widget should delete the decorations

Known issues:

• on re-open of find widget, decorations don't appear until user input/action #145630

[Tyriar]

Added myself as a tester despite doing a bit of the end work on it as I want to test it thoroughly anyway.