Add category spending report (#1382)

...s/desktop-client/src/components/accounts/MobileAccount.js

.../desktop-client/src/components/accounts/MobileAccounts.js

...top-client/src/components/autocomplete/CategorySelect.tsx

...esktop-client/src/components/reports/CategorySelector.tsx

...desktop-client/src/components/reports/CategorySpending.js

packages/desktop-client/src/components/reports/Header.js

packages/desktop-client/src/components/reports/Overview.js

...ges/desktop-client/src/components/reports/ReportRouter.js

...t/src/components/reports/graphs/CategorySpendingGraph.tsx

...op-client/src/components/reports/graphs/NetWorthGraph.tsx

...mponents/reports/graphs/category-spending-spreadsheet.tsx

...s/desktop-client/src/components/reports/graphs/common.tsx

...s/desktop-client/src/components/settings/Experimental.tsx

packages/desktop-client/src/hooks/useCategories.ts

packages/desktop-client/src/hooks/useFeatureFlag.ts

packages/loot-core/src/types/prefs.d.ts

upcoming-release-notes/1382.md