Rename to ponylang-vscode-extension

[mfelsche]

as the extension names pony and ponylang are already taken on the vscode marketspace.

The alternative name pony-lsp was considered to be too specific, as the extension does a little more.

[SeanTAllen]

when this merges we should:

• update EDITORS.md in ponyc to point at this, not the old npruhs extension
• the README (lines 16, 19) should be updated to account for this change as part of the PR
• the Makefile (line 15 and 21) as well
• package-lock.json lines 2, 8: still says "name": "pony"

[SeanTAllen]

I left a comment with the things in repo (and outside) that need to change with this.