Refactor SpiUtil to improve mocking

[jack-berg]

Working on file configuration stuff, which will have to load SPI implementations like autoconfigure. We currently have most of our SPI related code in static methods in SpiUtil, which makes testing / mocking difficult.

This refactors the SPI accessors in an SpiHelper class. SpiHeler accepts a ClassLoader as an argument, and can be passed around autoconfigure (and soon file configuration interpretation code) in place of ClassLoader. It contains accessors for the various ways we load SPI implementations (named and configurable via ConfigProperties, orders, and a plain list).

Much better for mocking in tests.

This is a strict refactor.

[codecov]

Codecov Report

Patch coverage: 97.36% and project coverage change: +0.01% 🎉

Comparison is base (90ab366) 91.31% compared to head (4be082b) 91.33%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #5679      +/-   ##
============================================
+ Coverage     91.31%   91.33%   +0.01%     
- Complexity     4980     4989       +9     
============================================
  Files           554      554              
  Lines         14735    14769      +34     
  Branches       1376     1378       +2     
============================================
+ Hits          13456    13489      +33     
  Misses          883      883              
- Partials        396      397       +1     

Files Changed	Coverage Δ
...ry/sdk/autoconfigure/internal/NamedSpiManager.java	100.00% <ø> (ø)
...nfigure/AutoConfiguredOpenTelemetrySdkBuilder.java	94.40% <85.71%> (ø)
.../autoconfigure/LogRecordExporterConfiguration.java	100.00% <100.00%> (ø)
...sdk/autoconfigure/LoggerProviderConfiguration.java	100.00% <100.00%> (ø)
.../sdk/autoconfigure/MeterProviderConfiguration.java	100.00% <100.00%> (ø)
...sdk/autoconfigure/MetricExporterConfiguration.java	100.00% <100.00%> (ø)
...try/sdk/autoconfigure/PropagatorConfiguration.java	100.00% <100.00%> (ø)
...metry/sdk/autoconfigure/ResourceConfiguration.java	94.73% <100.00%> (ø)
...y/sdk/autoconfigure/SpanExporterConfiguration.java	100.00% <100.00%> (ø)
...sdk/autoconfigure/TracerProviderConfiguration.java	100.00% <100.00%> (ø)
... and 1 more

... and 10 files with indirect coverage changes

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[jkwatson]

no objection from me