fix(freebusy): fixes busy status not shown in thunderbird

[SurajDadral]

Fixes issue #701

[phil-davis]

@SurajDadral there are various unit tests that expect the previous behavior. Please have a look and adjust those so that the tests pass.

[SurajDadral]

@phil-davis updated unit tests, now composer test shows all tests are passed

[SurajDadral]

@phil-davis pushed same changes to 4.5 branch in my fork, let me know if I should create MR from that branch instead: https://github.com/sabre-io/vobject/compare/4.5...nexbro:vobject:4.5?expand=1

[phil-davis]

pushed same changes to 4.5 branch in my fork, let me know if I should create MR from that branch instead

After merging this, I will backport to the relevant supported release branches.

[phil-davis]

@staabm @DeepDiver1975
I made some notes at #701 (comment)

The current behavior of the server code is within the RFC - if FBTYPE is BUSY then it gets left off, because that is the default anyway. But it is reported that Thunderbird does not "cope" with that (it should - I wonder when Thunderbird started having this problem?)

Anyway, we could change the server, as per this PR, to do more than the strict minimal behavior as per the RFC, and let it send FBTYPE=BUSY even though it is the default. Clients should not have a problem with that (but who knows if there is some client that will complain about getting an unnecessary FBTYPE=BUSY )

Opinions please.

[staabm]

//cc @evert

[evert]

My opinion is that some effort should be made to report the bug in the project that has the bug! If that's not going anywhere then consider a workaround.

I don't think the change is super risky, but there's a much greater benefit to fix the root problem for the ecosystem as a whole than to admit defeat and assume clients will always remain broken.

[phil-davis]

I asked for a link to the Thunderbird bug/problem report:
#701 (comment)