[Experimental transpiler] support for setMetadata and getMetadata

[pabloalmunia]

We have beed added support for the new setMetadata() and getMetadata() into the experimental transpiler:

https://javascriptdecorators.org/

Please, share we us your opinion about the transpiler result.

[pabloalmunia]

We have reviewed the experimental transpiler with just over 170 test cases and have detected some bugs that have already been corrected into the 0.3.1 version.