Revert "Drop support for initialization with another money object."

[elfassy]

Reverts #279

Why

Removing the ability from Money.new to accept a money object is creating toil on multiple repos, including core, preventing the gem to be updated
ex: https://github.com/Shopify/shipify/pull/27262

It will also allow us to stay consistent with expectations shared with the RubyMoney gem https://github.com/RubyMoney/money/blob/main/spec/money_spec.rb#L57-L60

We still want to prevent changing the currency as mentioned in the original PR description.

What

• allow Money.new to accept a money object (revert)
• raise if Money.new is passed a money object with a different currency, that would cause the currency to change

[fredericboivin]

Was it intentional to remove Gemfile.lock from gitignore? Historically this is something that gems avoided to prevent situations where our Gemfile.lock unnecessarily pins versions that are incompatible with the dependencies of client apps instead of letting bundler figure it out

[mkorostoff-shopify]

Looks good to me! The one thing I'm uncertain about is how/where the version numbering should be configured. This would would go in 2.2.0 (not 2.1.0 as shown in the lockfile) but we could make a separate PR for that.