Additional template lint validations and editor updates

Based on feedback:

Validate template (dev) name: letter, followed by letter/number/_, no _, no ending in , maxLength 80
Set label maxLength 80
Set description maxLength to 255
Include default visibility in New Page snippets in ui.json
Validate assetVersion is 36.0+, and a whole or *.0 number
Template (dev) name must match folder name
Only show support field completions for variableType type

forcedotcom / analyticsdx-vscode