feat(core): Query builder

[yagodorea]

Pull Request Checklist

• Have you added new tests to prevent regressions?
• If a documentation update is necessary, have you opened a PR to the documentation repository? docs: query builder sequelize/website#804
• Did you update the typescript typings accordingly (if applicable)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
• Does the name of your PR follow our conventions?

Description of Changes

Adds a simple query builder to sequelize static models. Basic functionality:

• Model.select() -> will instantiate the query builder for chaining
• .attributes(['a', 'b']) -> select attributes
• .where({c: true, d: 1}) -> specify where conditions
• .getQuery() -> return plain SQL
• Add an .execute() method that will run the raw sql instead of returning it
• Support .limit() and .offset()
• Support .orderBy([['a', 'DESC'], ['b', 'ASC']])
• Support .groupBy(['a', 'b', 1, 2])
• Support .having()
• Support .andHaving()
• Support .include() with custom join logic

Future improvements/additions:

• Support returning the Model objects instead of raw result
• Support .andWhere using Sequelize.where(col, op, value), Sequelize.literal() and WhereBrackets as per proposal
• Support .orWhere, block simultaneous usage with .andWhere
• Allow QueryBuilder on right-hand side of where options as a subquery/literal (DynamicValues?)
• Support CTEs