Add go to definition to I18n translations

[domingo2000]

When using I18n, it will be useful to have GoToDefinition support. Improving the developer experience when working with translations.

Examples:

• I18n.t("some-key") in .erb and .rb file.
• I18n.translate("some-key") in .erb and .rb file.

Both should go to the definition(s) of that translation(s)

Some considerations:

1. Changes in the yaml files that have the translations should be considered, the definition must be synced between the I18n backend when their sources changes (exampel: if I change a yaml file es.yml, the go to definition should change too).
2. I18n could have different/custom translation backends.

My take on this is that this could be implemented in the following way:

1. Make I18n have the metadata of where is each translation located. This should be opt-in so we only turn it on in development mode, so now the translation I18n.t("key") gives the pair (value, source_location) instead of just the value. This could be done via contribution to I18n or monkey patching in this addon, i prefer the first aproach.
2. Use the same strategy as Add hover on i18n translations #640 but use a new request that use this new metadata from the I18n running in the rails background process to get the source_location of the translation in the go_to_definition_request.

The key is easily accessible by the AST tree in the I18n.t("string") call.