Merge release/dev16.3-preview1 to master

Merge remote-tracking branch 'dotnet/release/dev16.3-preview1' into merges/release/dev16.3-preview1-to-master

Make Field Readonly - Keep leading trivia

Merge pull request #36903 from jasonmalinowski/fix-diagnostic-options-not-flowing-through-recoverable-trees

Don't lose tree DiganosticOptions when we recover or replace a tree

made error and todo list initialization lazy

Require System.Index/Range to be present to offer to use the new language features.

Unskip BasicEditAndContinue Tests

Update .NET Core SDK Url in build on Windows instructions

Merge release/dev16.3-preview1 to master

Merge all indentation related code into one service.

Preserve local function preceding whitespace for Issue #35489

Relax the rule that tries to get rid of this./me. in Roslyn code.

This reverts commit c30fd2bb.

We were not passing through DiagnosticOptions when we created a
recoverable tree or when we called Solution.WithDocumentSyntaxRoot. This
implementation takes a straightforward approach that we simply hold
onto the DiagnosticOptions in the process (rather than recovering it);
we could improve on that but it makes things a bit trickier since
DiagnosticOptions would have to be fetched on demand.

Fixes https://github.com/dotnet/roslyn/issues/26391

Consistently name C#/VB editors

* Don't update analyzed nullability for param conversions
* Fix test types

Another thousand cleanup suggestions in IDE