build(lint): use changed lines instead of changed files to avoid false positives.

[Hweinstock]

Problem

Currently jscpd ci action filters on changed files in PR. This results in clones being returned from changes outside our changes (but within the same files).

jscpd is the most commonly failing CI task at the moment, so to keep CI green we want to reduce false positives.

Solution

• jscpd only lists clones that includes lines from the changed lines in the changed files.
• see https://github.com/aws/aws-toolkit-vscode/actions/runs/11799554967/job/32868336302?pr=5950 as an example failure.
• Included in this PR is a refactor of the action to simplify the bash scripting done in the action yml file.
• Also modifies action file to include manual "local" switch so that it can be run locally. (this was broken before)
• Some tests for the filterDuplicates.ts script to make future changes easier.

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License: I confirm that my contribution is made under the terms of the Apache 2.0 license.