Create a registry of code actions available instead of relying on diagnostics

[ferranbt]

Right now, the two code actions that we support (import libraries and create SPDX license) work as follow:

• During post-processing of the parsing contracts we check the diagnostics for these two errors.
• Create bespoke references for each error the FileCache object.
• Upon receiving code actions, check those references and create the actions accordinly.

Instead, we should create an array of code actions directly after parsing and check that directly. Note, this is how we are handling hints as well after we started to have more than one type.