time: Fix toml zoneinfo inconsistency

[satotake]

TOML's time representation has known issues about zoneinfo name such as PDT in hugo

• htime: set zone of datetime from from go-toml #9082
• hugolib: Add test case for #9082 #9982
• time.Format - timezone details missing with time_full and time_long with TOML dates  #8895
• Date format / timezone issue after remote build #9996

These are caused because

• TOML's time format has only offset
  • zoneinfo cannot be retrieved with offset value
• TZ environment variable can change the behaviour
• cast.ToTimeInDefaultLocationE may or may not use location arg

Given that hugo often is used on both local and remote machine, and as #9996 said hugo supports multilingual site generation,

• TZ envvar should not have any effect on this
  • Remote environments can be hard to debug
  • UPDATE: If the site config does not have timezone, use time.Local (exception)
    • see the comment
• If only timeZone is set explicitly in config file and offsets of
  time are matched with it, hugo should show zoneinfo
  • Otherwise, zoneinfo should not be displayed
• hugo should handle TOML's time object and time string equally

To meet these,

• assure to set location derived from conf to time of TOML if possible
• add tests

Close #9996

[bep]

@satotake thanks a lot for this. The code looks good to me, even if this "time landscape" is confusing me pretty hard.

@jmooring would you have time to take this PR for a spin and see if this fix makes sense to you?

[jmooring]

Sorry, but I don't understand the commit message "time: Fix toml zoneinfo inconsistency". This PR seems to be more about making this configuration work by ignoring the OS tzdata:

[languages.en]
languageCode = 'en-US'
languageName = 'English'
timeZone = 'America/Los_Angeles'
weight = 1

[languages.es]
languageCode = 'es-ES'
languageName = 'Espanol'
timeZone = 'Europe/Madrid'
weight = 2

Most sites have not set timeZone in site configuration, so this is a breaking change. The time zone abbreviations that are visible in <= v0.101.0 will not appear after this change unless site authors add timeZone to their site configuration. I'm fine with that, but we need to let people know.

[bep]

Most sites have not set timeZone in site configuration, so this is a breaking change.

We could possibly apply this fix only when the locale is established from config. Not sure.

[satotake]

Most sites have not set timeZone in site configuration, so this is a breaking change

We could possibly apply this fix only when the locale is established from config. Not sure.

It was my intention to show no zone info if config does not have timeZone (considering remote/local site building).
But I changed that. If the site config has no timeZone, try to use time.Local timezone.

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