Add ts-plugin to diagnostic sources

[yoavbls]

In the new official extension of Vue VSCode plugin, Hybrid mode is enabled by default,
which means that a TypeScript LSP Plugin publishes the diagnostics.
We didn't have ts-plugin in our diagnostic sources list so I add it.
and it solved #100 #101

[rchl]

Is ts-plugin the identifier of the vue ts plugin? Shouldn't it have more specific naming? Otherwise it could conflict with other extensions (not sure what the implications of that be).
@johnsoncodehk

[yoavbls]

@rchl I think ts-plugin is the identifier Volar or other TypeScript LSP Plugins use.
The plugin kicks in only for js/ts based files so I don't think it could conflict and work in improper places, but maybe @johnsoncodehk can clarify this