Update wpmreleasetoolkit to 12.0

[andrewdmontgomery]

Closes #389

Description

• Updates wpmreleasetoolkit to 12.0
  • This update contains breaking changes. We don't expect these changes to impact our usage.
• Updates Fastlane to the latest release

This prepares us for the upcoming release of 12.1, which will allow us to generate UTF-8 Localizable.strings files without our custom code.

Testing Steps

• CI should be 🟢

[wpmobilebot]

📲 You can test the changes from this Pull Request in Gravatar UIKit Prototype Build by scanning the QR code below to install the corresponding build.

	App Name	Gravatar UIKit Prototype Build
	Build Number	1210
	Version	1.0
	Bundle ID	com.automattic.gravatar-sdk-demo-uikit.prototype-build
	Commit	86941dd22b3a2c154e905e14f0f16254712e8479
	App Center Build	Gravatar SDK Demo - UIKit #102

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Gravatar SwiftUI Prototype Build by scanning the QR code below to install the corresponding build.

	App Name	Gravatar SwiftUI Prototype Build
	Build Number	1210
	Version	1.0
	Bundle ID	com.automattic.gravatar-sdk-demo-swiftui.prototype-build
	Commit	86941dd22b3a2c154e905e14f0f16254712e8479
	App Center Build	Gravatar SDK Demo - SwiftUI #101

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[AliSoftware]

@andrewdmontgomery release-toolkit version 12.1 has now been released with the new option for output_encoding.