Convert HideAdvancedMembers option to editorconfig option

[tmat]

Change the editorconfig name of the option from dotnet_hide_advanced_members_in_completion to dotnet_hide_advanced_members.

Add new section ".NET Code Actions" to editorconfig, so that the option is serialized into editorconfig like so:

#### .NET Code Actions ####

# Type members
dotnet_hide_advanced_members = true|false

A follow-up PR (#74376) we will add a couple of more options to this group:

dotnet_member_insertion_location = with_other_members_of_the_same_kind | at_the_end
dotnet_property_generation_behavior =  prefer_throwing_properties | prefer_auto_properties

Move HideAdvancedMembers option to a new MemberDisplayOptions struct and add extension methods to retrieve it from document.
Replace SignatureHelpOptions with MemberDisplayOptions as it only contains HideAdvancedMembers.
Add GetAddImportOptionsAsync extension method to follow the established pattern.
Remove AddMissingImportsOptions.

[tmat]

@dotnet/roslyn-ide @sharwell @Cosifne @CyrusNajmabadi ptal