Improve completion based on grammar with snippets

[angelozerr]

It should be nice to provide the capability to override completion item based on grammar with snippets.

Here a demo with dependency completion with pom.xml:

• the first completion item comes from LemMinx
• the second completion item comes from vscode-maven

The goal of this issue is to provide the same completion item of vscode-maven. The idea is to write a JSON snippet for dependency and use it to override the basic dependency completion item.

[tbazant]

+1 as that idea would improve the user experience that my 'DocBook snippet' extension for VSCode offers - see https://github.com/openSUSE/suse-vscode-doc/blob/main/extensions/docbook-snippets/snippets/snippets.code-snippets

[oscarlevin]

This would be great. In the mean time, I've done something similar for pretext-tools, although not on the LSP server side, which would probably be faster. See oscarlevin/pretext-tools#67