Added ts path mapping between packages

[trickstival]

What does this PR contain?

It just changes the @posva packages path to be mapped to the src instead of the declaration files generated by the build in the dist folder.

Before that, when ctrl clicking the package @posva/vuefire-core inside another package files, it
redirected to the dist folder. Now it goes to the src.

I also removed one import that was pointing to a dist folder inside the core package (idk why it was doing that).

Motivation

It was really frustrating to look after the core files while debugging and end up in a declaration file. This should make the code flow easier to understand by ctrl clicking.

Edit:
I noticed that #384 should have its problem fixed too

[trickstival]

For some reason, it complains about files not being included when testing, but all tsconfig.json files are already extending the one in the project root, and this one already includes packages/@posva/*/src.

[codecov-io]

Codecov Report

Merging #395 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #395   +/-   ##
=======================================
  Coverage   99.72%   99.72%           
=======================================
  Files          14       14           
  Lines         368      368           
  Branches       64       64           
=======================================
  Hits          367      367           
  Misses          1        1

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[posva]

I haven't checked yet but we have to make sure that some of the transpilation still happens:
#329 #332

[trickstival]

I haven't checked yet but we have to make sure that some of the transpilation still happens:
#329 #332

@posva I have checked the target in all yarn build scripts across the project and it's es5. I'm not sure if that's the kind of check I have to do.

[posva]

the best would be to test on IE and see if things are still working

[posva]

I think that in the future Vuefire should just be in one single package. This would remove so many existing problems we have with tooling...

[trickstival]

I think that makes sense, but would vuexfire be distributed in the same package too?

[posva]

yeah, everything in one tree-shakable package

[posva]

Thank you for this and sorry I never camke back to you @trickstival
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