Support selection range in snippets

[jdneo]

Here is a brief demonstration of the idea:

This feature might be used when the user forget to check null or something like that, and quickly wrap the code by a certain snippet.

The problem is that so far LSP does not support passing the selection information in code action param. So the server side cannot render the inserted text with the selections.

Can we first simply ignore the $TM_SELECTED_TEXT when rendering the insert text at the server side. Once the LSP supports it, we can then add them into it.

LSP related issue: microsoft/language-server-protocol#377 (comment)

[fbricon]

Can we first simply ignore the $TM_SELECTED_TEXT

Since this is not even referenced in jdt.ls, how do you propose to do that?

[jdneo]

How about:

1. Add $TM_SELECTED_TEXT into our server side templates
2. In beautifyDocument(String raw), detect the existence of $TM_SELECTED_TEXT and replace it with empty string.
3. The VS Code client will replace the $TM_SELECTED_TEXT to the actual code when inserting the snippet.

But I'm not sure if the other client supports the $TM_SELECTED_TEXT as well.

[fbricon]

Since $TM_SELECTED_TEXT is defined in the spec: https://microsoft.github.io/language-server-protocol/specifications/specification-3-14/#variables, jdt.ls can use it