Added support for this referencing inside firebase funcs

[trickstival]

The problem

When using typescript, it is not possible to access properties defined in this context. It warns that the defined props are not available in the scope with the message Error: "Property 'nameOfProp' doesn't exist on type Vue".

Proposed solution

I augmented VueConstructor type so it passes default typings around on extend function (which doesn't happen in Vue itself) and passed a CombinedInstance type as this for the firestore and firebase functions.

I'm not sure if that's a good approach, cause it messes up with Vue module definition.
If you know a better way of implementing this, pls share.

Still not fixed

• I haven't figured out yet how to infer methods, data and computed properties types. For now, it only infers prop types and treats everything else as any

fix #399

[codecov-io]

Codecov Report

Merging #407 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #407   +/-   ##
=======================================
  Coverage   99.72%   99.72%           
=======================================
  Files          14       14           
  Lines         368      368           
  Branches       64       64           
=======================================
  Hits          367      367           
  Misses          1        1

Impacted Files	Coverage Δ
packages/vuefire/src/index.ts	100% <ø> (ø)	⬆️
packages/vuefire/src/rtdb.ts	100% <ø> (ø)	⬆️
packages/vuefire/src/firestore.ts	100% <ø> (ø)	⬆️

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[TomKaltz]

What's the status here?

[trickstival]

I think there's a coverage problem, but I'm still waiting for the review

[posva]

I'm not sure if there is a way to also type the methods and other properties. Maybe using the type of a method in a Vue instance we can infer this correctly. Having a partial type only is not enough

The coverage difference doesn't matter :)

[trickstival]

I'm not sure if I get what you mean by using the type of a method in a Vue instance. The typing code is getting pretty hard to follow.

[posva]

The typing code is getting pretty hard to follow.

yeah, I know...

I mean that doing this.myMethod() should also work but currently it doesn't

[posva]

Thank you for this and sorry I never came back again
This ended up changing quite a lot and this PR isn't relevant anymore. The progress of the latest release can be followed at #1241