More Corelib cleanup (dotnet/coreclr#26872)

More Corelib cleanup (dotnet/coreclr#26872)

* Remove unnecessary asserts

* Make several classes static

* Use is instead of as+null check

* Use T? instead of Nullable<T>

* more static classes

* Mark locals as const

* Merge declaration and initialization of some variables

* Remove unnecessary casts

* Remove unnecessary "unsafe"s

* Simplify several lambda expressions

* Remove redundant parentheses

* Remove redundant '== true'

* Remove redundant empty lines

* Simplify boolean comparison with '== false'

* Replace if-statement with return statement

* Use while for infinite loop

* Add static to all partial static class declarations

* Use ++/-- operator instead of assignment

* Use string.IsNullOrEmpty

* Use coalesce expression

* Simplify lazy initialization

* Use coalese expression

* Join string expressions

* Use regular string literal instead of verbatim string literal

* Optimize StringBuilder.Append calls

* Remove redundant assignment

* Remove unnecessary unsafe context

* Merge processor directives

* Use String.Equals instead of String.Compare

* Use Debug.Fail instead of Debug.Assert(false

* Remove Attribute suffix

* Use predefined type

* Use compound assignment

* Use while statement to create an infinite loop

* Remove redundant base ctor call

* Avoid using catch (Exception)

* Remove empty regions

* Span comparison to null

* Avoid unnecessary boxing of value type

* Expression is always equal to 'true'

* Remove unused method

* update coalesce assignment

* fix unsafe

* fix redundant parens

* Fix whitespace errors introduced

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>