fix: Expose FlushAsync to intellisense

[bruno-garcia]

Resolves #360

[codecov-io]

Codecov Report

Merging #362 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #362   +/-   ##
=======================================
  Coverage   93.32%   93.32%           
=======================================
  Files         117      117           
  Lines        2802     2802           
=======================================
  Hits         2615     2615           
  Misses        187      187

Impacted Files	Coverage Δ
src/Sentry/SentrySdk.cs	100% <ø> (ø)	⬆️

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