in XLinq XObject there is no need to instantiate XObjectEventArgs every time.
Cache only resolved types not expression to report correct error location. Fixes #15035
Inline more is instance checks
reduce memory use on Attribute() caused by Attributes().
Fallback to $LANG if $LC_ALL isn't set.

Fixes: https://bugzilla.xamarin.com/show_bug.cgi?id=15214

This is a regression introduced in be532638.

Xamarin.Android assumes that the $LANG environment variable can be
used to control System.Globalization.CultureInfo.CurrentCulture,
setting LANG based on the current Java locale.

This was broken in be532638 because $LANG was no longer being checked
to determine the default locale, as $LC_ALL was not set.

Fix the fallback logic so that $LANG is checked when $LC_ALL is not.
Element() and Elements() could also reduce use of extraneous iterators.
[System.ComponentModel.DataAnnotations] Implemented EmailAddressAttribute.IsValid()
Make Task.Delay more reliable. Fixes #14585
Adds async type inference of void return type. Fixes #15238
Minor fix to avoid ArgumentOutOfRangeException

When the file is empty, data[0] would throw and swallow the original exception.
Release continuation ancestor before running. Fixes #15036
Allow to queue multicast delegates in thread-pool
Remove redundant initialization
Simplify work item registration for internal work items
Cleanup redundant code
Enum IConvertible can convert to same enum or System.Enum. Fixes #15289
    anonymous: move counters to TypeContainer

    With the anonymous counters on ModuleContainer,
    anonymous method and type names will be generated
    in a way that depends on the order of the sources
    passed to mcs. This can cause undesirable API
    and IL differences.

    Moving the counters to TypeContainer instead
    avoids this issue.
[monodoc] Ensure we don't try to use <Parameters> when it might be null. Fixes Gendarme doc generation.
[monodoc] Add a test for ba222d4eb939ef097dd2b77b1fea5c3b8a60b310
[monodoc] Support fields that match operator naming convention