Move Linked variables code into its own component

...iew/test_cases_view/test_case_selected/PaySlipView.svelte

...ew/test_cases_view/test_case_selected/TestCaseView.svelte

...onents/legislation_view/parameters/LinkedVariables.svelte

src/lib/decompositions.ts

src/lib/iterators.ts

src/routes/+page.svelte