Remove suppressImplicitAnyIndexErrors from tsconfig

[raineorshine]

Please:

• Make your pull request atomic, fixing one issue at a time unless there are many relevant issues that cannot be decoupled.
• Provide a test case & update the documentation in the Readme.md

This PR is a continuation of the Typescript v5 upgrade (#564) that factors out the implicit use of index signatures, allowing suppressImplicitAnyIndexErrors and ignoreDeprecations to be removed from the tsconfig.

Due to the extensive use of indexing into interfaces (namely Definition), I have created a DefinitionIndex type that is a looser version of Definition allowing indexing. In other cases I needed to cast a type as a Record or cast a key as keyof Definition in order to allow the desired indexing.

Let me know if you know of a more elegant approach, or have any additional feedback.

[domoritz]

Thank you