Promote experimental Qute validation

[angelozerr]

The Qute validation manages syntax error and semantic error (like undefined varriable, unknown property, etc). But it has some limitation like:

• don't support infox notation
• don't support bracket notation for property (ex : item['name'])

It means that there are error although it should not have errors. See comments at redhat-developer/quarkus-ls#451 (comment)

@maxandersen suggested disable the Qute validation by default.

To promote that Qute support is able to validate Qute template, it should be nice to show the first time a popup which ask if user want to activate the Experimental Qute validation:

• yes -> will update the quarkus.tools.qute.validation.enabled settings to true
• no -> do nothing

@fbricon @rgrunber as the popup must be displayed just the first time after (and not open this popup each time we open vscode), I think we need to manage a flag like openPopupToActivateExperimentalQuteValidation, where can we store it? I think vscode-quarkus already manage this kind of flag if I remember to open Overview page of Quarkus (not sure for that).

[fbricon]

you can use globalState to store the information. See https://stackoverflow.com/a/51822055/753170