fix: change window and document DOM access to self checks for SW context

[krissvaa]

Fixes #2867

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.54%. Comparing base (c1245de) to head (cf3a028).

Files with missing lines	Patch %	Lines
packages/ts/frontend/src/Connect.ts	50.00%	0 Missing and 1 partial ⚠️
packages/ts/frontend/src/CookieManager.ts	0.00%	0 Missing and 1 partial ⚠️
packages/ts/frontend/src/FluxConnection.ts	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2900      +/-   ##
==========================================
- Coverage   92.65%   92.54%   -0.11%     
==========================================
  Files          83       83              
  Lines        2831     2832       +1     
  Branches      729      732       +3     
==========================================
- Hits         2623     2621       -2     
  Misses        156      156              
- Partials       52       55       +3     

Flag	Coverage Δ
unittests	92.54% <40.00%> (-0.11%)	⬇️

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[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[Lodin]

I'd suggest using globalThis across the code. It's guaranteed to work in any environment