feat(AgmMarker): add dblclick observable

[DefJunx]

add and manage double click event for marker

fixes #1601

I've added the dblclick event from google maps to the AgmMarker directive, following the structure used for the other events. Please note I didn't add any test case, as I wouldn't know what to test for (also, other events do not have a test either).

Let me know if there's something to fix.

[codecov]

Codecov Report

Merging #1739 into master will decrease coverage by 0.04%.
The diff coverage is 10.52%.

@@            Coverage Diff             @@
##           master    #1739      +/-   ##
==========================================
- Coverage   47.73%   47.68%   -0.05%     
==========================================
  Files          41       41              
  Lines        1835     1839       +4     
  Branches      167      167              
==========================================
+ Hits          876      877       +1     
- Misses        955      958       +3     
  Partials        4        4

Impacted Files	Coverage Δ
packages/core/directives/marker.ts	37.06% <10.52%> (-0.44%)	⬇️

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[fransyozef]

I see this feature is merged with master. But when I instal the package (via npm), I don't see the changes in the .ts file on my local. My package-lock.json resolves to version 1.0.0

    "@agm/core": {
      "version": "1.0.0",
      "resolved": "https://registry.npmjs.org/@agm/core/-/core-1.0.0.tgz",
      "integrity": "sha512-tgrobTyAHCZ3cdi21IdiBafiHLxsC5/6ncq6+f9RV+HrLg0XDuk+DA7upfdE34o2Ui3fNRDYDIgExRVFLsSPCw==",
      "requires": {
        "tslib": "^1.9.0"
      }
    },

[ghost]

This will be released in 1.1.0