Make the time zone resolver plugable

[minichma]

This PR implements several improvements related to resolving time zones:

• Fix test cases so they use well defined and known time zone IDs, so they don't fall back to the system's local TZ
• Stop falling back to the local TZ if the specified TZ is unknown. Its more than likely that in most cases the fallback is not what is expected/desired by the user.
• Make the time zone resolving functionality plugable

[sonarqubecloud]

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 SonarQube Cloud

[codecov]

Codecov Report

Attention: Patch coverage is 68.29268% with 13 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
Ical.Net/DefaultTimeZoneResolver.cs	68%	3 Missing and 8 partials ⚠️
Ical.Net/CalendarComponents/VTimeZone.cs	33%	2 Missing ⚠️

❌ Your patch status has failed because the patch coverage (68%) is below the target coverage (80%). You can increase the patch coverage or adjust the target coverage.
❌ Your project status has failed because the head coverage (66%) is below the target coverage (80%). You can increase the head coverage or adjust the target coverage.

@@         Coverage Diff         @@
##           main   #732   +/-   ##
===================================
  Coverage    66%    66%           
===================================
  Files       103    105    +2     
  Lines      4644   4645    +1     
  Branches   1152   1154    +2     
===================================
+ Hits       3064   3066    +2     
+ Misses     1144   1143    -1     
  Partials    436    436           

Files with missing lines	Coverage Δ
Ical.Net/TimeZoneResolvers.cs	100% <100%> (ø)
Ical.Net/Utility/DateUtil.cs	48% <100%> (-8%)	⬇️
Ical.Net/CalendarComponents/VTimeZone.cs	73% <33%> (ø)
Ical.Net/DefaultTimeZoneResolver.cs	68% <68%> (ø)

[minichma]

Relates to the discussion in #606 (reply in thread)

[axunonb]

👍

[axunonb]

Great idea!

[minichma]

Great idea!

Thanks and thanks for the review! Having global static parameters is always a somewhat poor design but in this case it seems to be the best short term solution without refactoring the whole evaluation code. At least for our project its a viable workaround. Could/should be improved in v6.