Merge user languages from initialization options and include languages

[thecrypticace]

Before v0.12.x we'd look at the tailwindCSS.includeLanguages setting in the extension, populate the userLanguages initialization option, and start the server. This setup necessitated a restart of the process whenever this setting changed. In v0.12.x we changed this so that we'd request the user's languages from the settings instead from the initiialization options. This allows us to keep the server running even when the settings change.

As part of this, for attempted backwards compatability, in v0.12.x (language server v0.0.16+) we'd still look at the userLanguages initialization option if it was present and only use it if no tailwindCSS.includeLanguages setting was present for a given workspace folder. However, it appears that this setting may end up populated and we'd ignore the userLanguages setting altogether when we shouldn't have.

To fix this we're going to merge in the userLanguages setting from the initialization options with the tailwindCSS.includeLanguages setting if present. Any mappings from settings will take precedence over those from the userLanguages initialization option.

I'm also explicitly warning when the userLanguages initialization option is present and noting it as a deprecated feature and telling users to use the tailwindCSS.includeLanguages setting instead.

Fixes #1002

• Add tests showing that language mappings are merged rather than replaced
• Test against the project in the aforementioned issue