Move tests to root directories

[becca-bailey]

This is the initial work to move test files into the packages they are testing. I ran into some complications around build config, detailed in comments below.

[ryan-roemer]

LGTM! (But I've only done a quick skim -- let's see what @scottrippey says :) )

[becca-bailey]

@scottrippey I think there is still an issue here where index.d.ts files are not getting copied correctly anymore. I'm investigating now!

[scottrippey]

Hard work, but good job!
Runs well locally.
Once the build is passing LGTM!

[ryan-roemer]

Notes for later -- here are all of our relative imports from tests:

$ find packages -name "*.test.*" -exec grep -rn "from \"./" {} \;
packages/victory-bar/src/victory-bar.test.js:5:import VictoryBar from "./victory-bar";
packages/victory-bar/src/victory-bar.test.js:6:import Bar from "./bar";
packages/victory-bar/src/geometry-helper-methods.test.js:1:import { circle, point } from "./geometry-helper-methods";
packages/victory-bar/src/bar.test.js:5:import Bar from "./bar";
packages/victory-stack/src/victory-stack.test.js:8:import VictoryStack from "./victory-stack";
packages/victory-voronoi/src/victory-voronoi.test.js:4:import Voronoi from "./voronoi";
packages/victory-voronoi/src/victory-voronoi.test.js:5:import VictoryVoronoi from "./victory-voronoi";
packages/victory-area/lib/area.test.js:2:import Area from "./area";
packages/victory-area/lib/helper-methods.test.js:1:import { getDataWithBaseline } from "./helper-methods";
packages/victory-area/es/area.test.js:2:import Area from "./area";
packages/victory-area/es/helper-methods.test.js:1:import { getDataWithBaseline } from "./helper-methods";
packages/victory-area/src/area.test.js:2:import Area from "./area";
packages/victory-area/src/helper-methods.test.js:1:import { getDataWithBaseline } from "./helper-methods";
packages/victory-scatter/src/helper-methods.test.js:1:import * as Helpers from "./helper-methods";
packages/victory-scatter/src/victory-scatter.test.js:5:import VictoryScatter from "./victory-scatter";
packages/victory-brush-container/src/brush-helpers.test.js:1:import Helpers from "./brush-helpers";
packages/victory-core/src/victory-animation/util.test.tsx:2:import { victoryInterpolator } from "./util";
packages/victory-core/src/victory-accessible-group/victory-accessible-group.test.tsx:3:import { VictoryAccessibleGroup } from "./victory-accessible-group";
packages/victory-core/src/victory-util/axis.test.ts:4:import * as Axis from "./axis";
packages/victory-core/src/victory-util/axis.test.ts:5:import * as Scale from "./scale";
packages/victory-core/src/victory-util/data.test.tsx:3:import * as Data from "./data";
packages/victory-core/src/victory-util/domain.test.tsx:2:import * as Domain from "./domain";
packages/victory-core/src/victory-util/collection.test.ts:1:import * as Collection from "./collection";
packages/victory-core/src/victory-primitives/line.test.tsx:2:import { Line } from "./line";
packages/victory-core/src/victory-primitives/clip-path.test.tsx:4:import { ClipPath } from "./clip-path";
packages/victory-core/src/victory-label/victory-label.test.tsx:2:import { VictoryLabel } from "./victory-label";
packages/victory-core/src/victory-container/victory-container.test.tsx:2:import { VictoryContainer } from "./victory-container";
packages/victory-pie/src/slice.test.tsx:3:import Slice from "./slice";
packages/victory-pie/src/victory-pie.test.js:5:import Slice from "./slice";
packages/victory-pie/src/victory-pie.test.js:6:import VictoryPie from "./victory-pie";
packages/victory-candlestick/src/victory-candlestick.test.js:4:import Candle from "./candle";
packages/victory-candlestick/src/victory-candlestick.test.js:5:import VictoryCandlestick from "./victory-candlestick";
packages/victory-candlestick/src/candle.test.js:3:import Candle from "./candle";
packages/victory-candlestick/src/helper-methods.test.js:3:import { getData, getDomain } from "./helper-methods";
packages/victory-line/src/curve.test.tsx:2:import Curve from "./curve";
packages/victory-line/src/victory-line.test.js:5:import Curve from "./curve";
packages/victory-line/src/victory-line.test.js:6:import VictoryLine from "./victory-line";
packages/victory-selection-container/src/selection-helpers.test.js:4:import SelectionHelpers from "./selection-helpers";
packages/victory-chart/src/helper-methods.test.js:1:import { getChildComponents } from "./helper-methods";
packages/victory-histogram/src/victory-histogram.test.js:4:import VictoryHistogram from "./victory-histogram";
packages/victory-group/src/victory-group.test.js:4:import VictoryGroup from "./victory-group";
packages/victory-tooltip/src/victory-tooltip.test.js:2:import Flyout from "./flyout";
packages/victory-tooltip/src/victory-tooltip.test.js:3:import VictoryTooltip from "./victory-tooltip";
packages/victory-tooltip/src/flyout.test.js:2:import Flyout from "./flyout";
packages/victory-box-plot/src/victory-box-plot.test.js:3:import VictoryBoxPlot from "./victory-box-plot";
packages/victory-errorbar/src/error-bar.test.js:4:import ErrorBar from "./error-bar";
packages/victory-errorbar/src/victory-errorbars.test.js:5:import ErrorBar from "./error-bar";
packages/victory-errorbar/src/victory-errorbars.test.js:6:import VictoryErrorBar from "./victory-errorbar";
packages/victory-legend/src/victory-legend.test.js:4:import VictoryLegend from "./victory-legend";