[ML] Creating number utils package for roundToDecimalPlace function (#154910)

`roundToDecimalPlace` is used in ML and data visualiser packages and
soon aiops, so this PR moves it to a shared package.

x-pack/packages/ml/number_utils/README.md

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+# @kbn/ml-number-utils
+
+Utility functions for operations on numbers

x-pack/packages/ml/number_utils/index.ts

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+export { roundToDecimalPlace } from './src/round_to_decimal_place';

x-pack/packages/ml/number_utils/jest.config.js

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+module.exports = {
+  preset: '@kbn/test',
+  rootDir: '../../../..',
+  roots: ['<rootDir>/x-pack/packages/ml/number_utils'],
+};

x-pack/packages/ml/number_utils/kibana.jsonc

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+{
+  "type": "shared-common",
+  "id": "@kbn/ml-number-utils",
+  "owner": "@elastic/ml-ui"
+}

x-pack/packages/ml/number_utils/package.json

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+{
+  "name": "@kbn/ml-number-utils",
+  "private": true,
+  "version": "1.0.0",
+  "license": "Elastic License 2.0"
+}

x-pack/packages/ml/number_utils/src/round_to_decimal_place.test.ts

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { roundToDecimalPlace } from './round_to_decimal_place';
+
+describe('roundToDecimalPlace formatter', () => {
+  it('returns the correct format using default decimal place', () => {
+    expect(roundToDecimalPlace(12)).toBe(12);
+    expect(roundToDecimalPlace(12.3)).toBe(12.3);
+    expect(roundToDecimalPlace(12.34)).toBe(12.34);
+    expect(roundToDecimalPlace(12.345)).toBe(12.35);
+    expect(roundToDecimalPlace(12.045)).toBe(12.05);
+    expect(roundToDecimalPlace(12.005)).toBe(12.01);
+    expect(roundToDecimalPlace(12.0005)).toBe(12);
+    expect(roundToDecimalPlace(0.05)).toBe(0.05);
+    expect(roundToDecimalPlace(0.005)).toBe('5.00e-3');
+    expect(roundToDecimalPlace(0.0005)).toBe('5.00e-4');
+    expect(roundToDecimalPlace(-0.0005)).toBe('-5.00e-4');
+    expect(roundToDecimalPlace(-12.045)).toBe(-12.04);
+    expect(roundToDecimalPlace(0)).toBe(0);
+  });
+
+  it('returns the correct format using specified decimal place', () => {
+    expect(roundToDecimalPlace(12, 4)).toBe(12);
+    expect(roundToDecimalPlace(12.3, 4)).toBe(12.3);
+    expect(roundToDecimalPlace(12.3456, 4)).toBe(12.3456);
+    expect(roundToDecimalPlace(12.345678, 4)).toBe(12.3457);
+    expect(roundToDecimalPlace(0.05, 4)).toBe(0.05);
+    expect(roundToDecimalPlace(0.0005, 4)).toBe(0.0005);
+    expect(roundToDecimalPlace(0.00005, 4)).toBe('5.00e-5');
+    expect(roundToDecimalPlace(-0.00005, 4)).toBe('-5.00e-5');
+    expect(roundToDecimalPlace(0, 4)).toBe(0);
+  });
+});

x-pack/packages/ml/number_utils/src/round_to_decimal_place.ts

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+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+/**
+ * Rounds a number to a specified decimal place.
+ * If the specified number is undefined, an empty string is returned.
+ *
+ * @param num - number to round
+ * @param dp - decimal place, default value is 2
+ * @returns rounded number
+ */
+export function roundToDecimalPlace(num: number | undefined, dp: number = 2): number | string {
+  if (num === undefined) return '';
+  if (num % 1 === 0) {
+    // no decimal place
+    return num;
+  }
+
+  if (Math.abs(num) < Math.pow(10, -dp)) {
+    return Number.parseFloat(String(num)).toExponential(2);
+  }
+  const m = Math.pow(10, dp);
+  return Math.round(num * m) / m;
+}

x-pack/packages/ml/number_utils/tsconfig.json

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+{
+  "extends": "../../../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "target/types",
+    "types": [
+      "jest",
+      "node",
+      "react"
+    ]
+  },
+  "include": [
+    "**/*.ts",
+    "**/*.tsx",
+  ],
+  "exclude": [
+    "target/**/*"
+  ],
+  "kbn_references": []
+}