package.json: add missing transform variants for go.addTags

This simply allows in the settings.json or UI to use the missing 'lispcase', 'pascalcase' and 'keep'
transform options for the go.addTags command.

fixes #906

Change-Id: Ic1ef1fd6e9df755d048424275e75033914c91060
GitHub-Last-Rev: e181a58
GitHub-Pull-Request: #936
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/271357
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Trust: Suzy Mueller <suzmue@golang.org>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>

package.json

@@ -1689,7 +1689,10 @@
  "type": "string",
  "enum": [
  "snakecase",
- "camelcase"
+ "camelcase",
+ "lispcase",
+ "pascalcase",
+ "keep"
  ],
  "default": "snakecase",
  "description": "Transformation rule used by Go: Add Tags command to add tags"