use get_application_tracer in Elixir macros

[tsloughter]

The Erlang macros already properly use get_application_tracer.
The reason to use get_application_tracer is the macros lookup
the tracer for the particular application by module name.

[codecov]

Codecov Report

Merging #303 (f68e83a) into main (aa1ed7b) will not change coverage.
The diff coverage is n/a.

❗ Current head f68e83a differs from pull request most recent head 21bec97. Consider uploading reports for the commit 21bec97 to get more accurate results

@@           Coverage Diff           @@
##             main     #303   +/-   ##
=======================================
  Coverage   37.35%   37.35%           
=======================================
  Files          46       46           
  Lines        3266     3266           
=======================================
  Hits         1220     1220           
  Misses       2046     2046           

Flag	Coverage Δ
api	65.14% <ø> (ø)
elixir	14.59% <ø> (+0.18%)	⬆️
erlang	37.35% <ø> (ø)
exporter	19.75% <ø> (ø)
sdk	76.74% <ø> (ø)

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Impacted Files	Coverage Δ
...pps/opentelemetry_api/lib/open_telemetry/tracer.ex	37.50% <ø> (ø)

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[tsloughter]

We should maybe just get rid of the separation between tracers registered automatically for each application and those registered by the user, and then there would be only one "get tracer" function available anyway

[indrekj]

We should maybe just get rid of the separation between tracers registered automatically for each application and those registered by the user, and then there would be only one "get tracer" function available anyway

That would simplify things. Currently the tracers & application tracers part is quite confusing, at least to me.

[indrekj]

looks right to me, but I'll try it out in real code tomorrow

[tsloughter]

Agree it will probably confuse people.

Likely will merge this to get erlang and elixir to at least match asap and then have a PR for just getting rid of the separation.