fix: prefer globalThis instead of window to support webworkers

[legendecas]

Which problem is this PR solving?

• Loading package @opentelemetry/core in WebWorkers or ServiceWorkers encountered `ReferenceError: window is not defined.
• There is no window in either WebWorkers and ServiceWorkers.

Short description of the changes

• Preferring globalThis than window in getEnv.
• However, I didn't find a feasible way to test workers with karma :(.
• Ref: @opentelemetry/web does not work in web workers #1575
• Fixes: getEnv() for platform "browser" does not work with service workers #2211

[codecov]

Codecov Report

Merging #2465 (f713eb9) into main (9df2132) will increase coverage by 0.24%.
The diff coverage is 100.00%.

❗ Current head f713eb9 differs from pull request most recent head 5d78863. Consider uploading reports for the commit 5d78863 to get more accurate results

@@            Coverage Diff             @@
##             main    #2465      +/-   ##
==========================================
+ Coverage   92.69%   92.93%   +0.24%     
==========================================
  Files         129      135       +6     
  Lines        4503     4941     +438     
  Branches      973     1059      +86     
==========================================
+ Hits         4174     4592     +418     
- Misses        329      349      +20     

Impacted Files	Coverage Δ
...opentelemetry-core/src/platform/node/globalThis.ts	100.00% <100.00%> (ø)
...-sdk-trace-web/src/enums/PerformanceTimingNames.ts
...telemetry-sdk-trace-web/src/StackContextManager.ts
packages/opentelemetry-sdk-trace-web/src/types.ts
packages/opentelemetry-sdk-trace-web/src/utils.ts
...entelemetry-sdk-trace-web/src/WebTracerProvider.ts
.../opentelemetry-exporter-otlp-http/src/transform.ts	88.69% <0.00%> (ø)
...s/opentelemetry-instrumentation-fetch/src/fetch.ts	96.98% <0.00%> (ø)
...lemetry-exporter-otlp-http/src/transformMetrics.ts	95.71% <0.00%> (ø)
...kages/opentelemetry-exporter-otlp-http/src/util.ts	100.00% <0.00%> (ø)
... and 6 more

[obecny]

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