Simplify metric::data imports

[cijothomas]

In future, I expect to change the module path for metrics::data. This PR is a step1, to keep overall PRs smaller.

[codecov]

Codecov Report

Attention: Patch coverage is 71.76471% with 24 lines in your changes missing coverage. Please review.

Project coverage is 77.7%. Comparing base (57d1297) to head (76380cb).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
opentelemetry-stdout/src/metrics/exporter.rs	0.0%	17 Missing ⚠️
...-sdk/src/metrics/internal/exponential_histogram.rs	70.0%	3 Missing ⚠️
opentelemetry-sdk/src/metrics/mod.rs	95.6%	2 Missing ⚠️
opentelemetry-otlp/src/exporter/http/mod.rs	0.0%	1 Missing ⚠️
opentelemetry-proto/src/transform/metrics.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #2536     +/-   ##
=======================================
- Coverage   77.7%   77.7%   -0.1%     
=======================================
  Files        123     123             
  Lines      23057   23050      -7     
=======================================
- Hits       17938   17931      -7     
  Misses      5119    5119             

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