Convert createWindow parameters to options bag and add testid option

[sirtimid]

This PR refactors the createWindow function to use an options bag for its parameters, improving clarity and extensibility. Additionally, it introduces a new testId option, allowing customization of the data-testid attribute for the generated iframe.

We need this change in the MetaMask/ocap-kernel package (see issue), where the createWindow function is used, to set a different testId that doesn't conflict with the snaps iframe. This will ensure clear differentiation when using iframes across different packages.

Updated and expanded the test suite to cover the presence and absence of sandbox and testId attributes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.38%. Comparing base (7d15013) to head (d2828ba).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2765   +/-   ##
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  Coverage   94.38%   94.38%           
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  Files         478      478           
  Lines       10208    10209    +1     
  Branches     1557     1558    +1     
=======================================
+ Hits         9635     9636    +1     
  Misses        573      573           

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[rekmarks]

LGTM! I technically have the authority to approve this, but we'll wait for approval from someone on the Snaps team.