Launch KeePassXC password generator popup from the extension

[varjolintu]

Add support for launching the password generator popup from the browser and returning the generated password.
Removes all password related settings from BrowserSettings class.

Related KeePassXC-Browser PR: keepassxreboot/keepassxc-browser#1329

Fixes #6473.

Testing strategy

Manually.

Type of change

• ✅ New feature (change that adds functionality)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 12.82051% with 34 lines in your changes missing coverage. Please review.

Project coverage is 63.93%. Comparing base (9aa30c4) to head (fbd3495).
Report is 586 commits behind head on develop.

Files with missing lines	Patch %	Lines
src/browser/BrowserService.cpp	0.00%	21 Missing ⚠️
src/browser/BrowserAction.cpp	35.71%	9 Missing ⚠️
src/gui/PasswordGeneratorWidget.cpp	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6529      +/-   ##
===========================================
+ Coverage    63.77%   63.93%   +0.17%     
===========================================
  Files          330      330              
  Lines        41857    41750     -107     
===========================================
+ Hits         26691    26692       +1     
+ Misses       15166    15058     -108     

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[varjolintu]

Not working yet, even if I made the fixes. If the password dialog is closed, after that it doesn't fill anymore when launched again.

[varjolintu]

Fixed a bug where the signal was connected multiple times (on every new request). Moved the lambda to the constructor so we can make sure it's only connected once.

[droidmonkey]

This works REALLY well, great job @varjolintu. As a note, when you connect a lambda function to a signal, you need to provide a context (the third parameter in connect) to ensure the lambda is destroyed when the context is destroyed. I added it to BrowserService and BrowserAction calls for you.