refactor: update build process to enable tree shaking

[vlapo]

Hi folks,

long-awaited refactor is here. As PR #258 is pretty old I moved main @HonoluluHenk idea to this PR and improved build process.

What is done:

• each validator/decorator moved to separate file
• imports stay unchanged (main difference between this PR and Smaller bundle size #258) - import { IsString } from 'class-validator';
• build process using rollup - enable tree shaking

Breaking changes:

• breaking changes from validator@12.2.0 - will mentione in changelog later
• all validations (except system ones) are type ValidationTypes.CUSTOM_VALIDATION now - mostly internal change
• all validators from Validator class was removed - because of tree shaking. So you have to use:

import {isString} from "class-validator";
isString(1); // false

instead of:

import {Validator} from "class-validator";
// Validation methods
const validator = new Validator();
validator.isString(1); // false

TODO:

• try use validator lib tree shakeable feature and push bundle size down event more
• test with nestjs
• test, review and clean code
• update README.md and CHANGELOG.md

Testing:
This PR is published under class-validator@tree-shaking tag. I would like to ask everyone for help in testing and reviewing PR. I tested it on simple boilerplate angular 8 application and results are:

• Without @IsPhoneNumber validator used:
  • main-es5 bundle size before 891kB <-> after 256kB
  • main-es2015 bundle size before 859kB <-> after 221kB
• With @IsPhoneNumber:
  • main-es5 bundle size before 891kB <-> after 790kB
  • main-es2015 bundle size before 859kB <-> after 755kB

Close #258
Close #248
Close #247
Close #212

[vlapo]

class-validator@0.12.0-refactor.4 published. I updated rollup config a little bit and add .min.js bundle files.
@patrykkrawczyk thnx for pointing me to agadoo tool.

[github-actions]

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