Add time zone handling APIs

[BuddhiWathsala]

Purpose

Fixes ballerina-platform/ballerina-library#1059

Examples

Checklist

• Linked to an issue
• Updated the changelog
• Added tests

[codecov]

Codecov Report

Merging #337 (851aca6) into master (5353449) will increase coverage by 2.91%.
The diff coverage is 92.85%.

@@             Coverage Diff              @@
##             master     #337      +/-   ##
============================================
+ Coverage     88.81%   91.73%   +2.91%     
- Complexity       44       61      +17     
============================================
  Files            10       13       +3     
  Lines           304      363      +59     
  Branches         69       89      +20     
============================================
+ Hits            270      333      +63     
+ Misses           23       22       -1     
+ Partials         11        8       -3     

Impacted Files	Coverage Δ
...o/ballerina/stdlib/time/util/TimeValueHandler.java	50.00% <80.00%> (-26.20%)	⬇️
...main/java/io/ballerina/stdlib/time/util/Utils.java	85.10% <85.10%> (ø)
...na/stdlib/time/nativeimpl/TimeZoneExternUtils.java	87.50% <87.50%> (ø)
ballerina/time_apis.bal	100.00% <100.00%> (ø)
ballerina/time_types.bal	100.00% <100.00%> (ø)
...ava/io/ballerina/stdlib/time/nativeimpl/Civil.java	100.00% <100.00%> (+15.38%)	⬆️
...allerina/stdlib/time/nativeimpl/ExternMethods.java	98.43% <100.00%> (ø)
...java/io/ballerina/stdlib/time/nativeimpl/Zone.java	100.00% <100.00%> (ø)
.../java/io/ballerina/stdlib/time/util/Constants.java	100.00% <100.00%> (ø)
... and 1 more

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[daneshk]

isn't this a fixed offset?

[BuddhiWathsala]

I initially thought that too. But seems it is not a fixed offset.

ZoneId.of("Asia/Colombo").normalized().getRules().isFixedOffset(); // Returns false

And even the IANA time zone dataset has these changes as well.

# Sri Lanka

# From Paul Eggert (2013-02-21):
# Milne says "Madras mean time use from May 1, 1898.  Prior to this Colombo
# mean time, 5h. 4m. 21.9s. F., was used."  But 5:04:21.9 differs considerably
# from Colombo's meridian 5:19:24, so for now ignore Milne and stick with
# Shanks and Pottenger.

# From Paul Eggert (1996-09-03):
# "Sri Lanka advances clock by an hour to avoid blackout"
# (<http://www.virtual-pc.com/lankaweb/news/items/240596-2.html>, 1996-05-24,
# no longer available as of 1999-08-17)
# reported "the country's standard time will be put forward by one hour at
# midnight Friday (1830 GMT) 'in the light of the present power crisis'."
#
# From Dharmasiri Senanayake, Sri Lanka Media Minister (1996-10-24), as quoted
# by Shamindra in Daily News - Hot News Section
# <news:[email protected]> (1996-10-26):
# With effect from 12.30 a.m. on 26th October 1996
# Sri Lanka will be six (06) hours ahead of GMT.

# From Jesper Nørgaard Welen (2006-04-14), quoting Sri Lanka News Online
# <http://news.sinhalaya.com/wmview.php?ArtID=11002> (2006-04-13):
# 0030 hrs on April 15, 2006 (midnight of April 14, 2006 +30 minutes)
# at present, become 2400 hours of April 14, 2006 (midnight of April 14, 2006).

# From Peter Apps and Ranga Sirila of Reuters (2006-04-12) in:
# http://today.reuters.co.uk/news/newsArticle.aspx?type=scienceNews&storyID=2006-04-12T172228Z_01_COL295762_RTRIDST_0_SCIENCE-SRILANKA-TIME-DC.XML
# [The Tamil Tigers] never accepted the original 1996 time change and simply
# kept their clocks set five and a half hours ahead of Greenwich Mean
# Time (GMT), in line with neighbor India.
# From Paul Eggert (2006-04-18):
# People who live in regions under Tamil control can use [TZ='Asia/Kolkata'],
# as that zone has agreed with the Tamil areas since our cutoff date of 1970.

# From Sadika Sumanapala (2016-10-19):
# According to http://www.sltime.org (maintained by Measurement Units,
# Standards & Services Department, Sri Lanka) abbreviation for Sri Lanka
# standard time is SLST.
#
# From Paul Eggert (2016-10-18):
# "SLST" seems to be reasonably recent and rarely-used outside time
# zone nerd sources.  I searched Google News and found three uses of
# it in the International Business Times of India in February and
# March of this year when discussing cricket match times, but nothing
# since then (though there has been a lot of cricket) and nothing in
# other English-language news sources.  Our old abbreviation "LKT" is
# even worse.  For now, let's use a numeric abbreviation; we can
# switch to "SLST" if it catches on.

# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
Zone	Asia/Colombo	5:19:24 -	LMT	1880
			5:19:32	-	MMT	1906        # Moratuwa Mean Time
			5:30	-	+0530	1942 Jan  5
			5:30	0:30	+06	1942 Sep
			5:30	1:00	+0630	1945 Oct 16  2:00
			5:30	-	+0530	1996 May 25  0:00
			6:30	-	+0630	1996 Oct 26  0:30
			6:00	-	+06	2006 Apr 15  0:30
			5:30	-	+0530