feature request: add a TM_FILENAME_BASE and TM_FILENAME_EXT or similar variables for snippets

[dmccaffery]

• VSCode Version:

$ code --version
1.11.2
6eaebe3b9c70406d67c97779468c324a7a95db0e

• OS Version:

$ sw_vers
ProductName:	Mac OS X
ProductVersion:	10.12.4
BuildVersion:	16E195

Feature Request:

Currently, the TM_FILENAME includes the extension and their is no way to strip this within a snippet. For snippets such as those that insert a class definition in languages where the file name is conventionally relevant to the class / module / function within, it would be great to get access to the filename with the extension stripped.

I can't think of a scenario with the filename extension is relevant, honestly, but if you're going to split the string on the first occurrence of a ., you might as well join everything to the right of that dot and have a var for that as well. :)

[jrieken]

Transformations is what we need. Closing as dupe of #6920