fix(terminal): implement correct and secure TerminalBuffer.getLines()

[Fangoling]

What it does

Fixes: #16971
Changes to the terminal buffer implementation:

• Utilizes start parameter

• Returns empty array if the start parameter is out of bounds

• Checks if the line is null before calling translate to String

• Add optional parameter trimRight to allow the user to trim whitespace at the end of each line

• Fixes the call to getLines in terminal-main.ts in the plugin ext extension: it was previously expecting the output of the terminal extension to be in chronological error, which did not fail as the start parameter was not used

How to test

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

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