Add autocompletion for base method calls on virual method overrides

[MightyPrinny]

Issue Description

On visual studio and monodevelop when you override a method, a call to the base method is automatically added, but on vscode with this extension it has to be added manually.

Steps to Reproduce

Override a virtual method.

Expected Behavior

When a method override is added, a call to the base method should be added automatically or there could be an autocompletion option available after typing "base." .

Actual Behavior

Nothing happens

Logs

OmniSharp log

Post the output from Output-->OmniSharp log here

C# log

Post the output from Output-->C# here

Environment information

VSCode version: 1.43.0
C# Extension: 1.21.15

Mono Information

OmniSharp using global mono :6.8.0

Dotnet Information

.NET Core SDK (reflecting any global.json): Version: 3.0.103 Commit: b7ef045669

Runtime Environment:
OS Name: debian
OS Version: 10
OS Platform: Linux
RID: debian.10-x64
Base Path: /usr/share/dotnet/sdk/3.0.103/

Host (useful for support):
Version: 3.0.3
Commit: c03f2fe626

.NET Core SDKs installed:
2.2.402 [/usr/share/dotnet/sdk]
3.0.103 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.2.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.2.8 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.2.8 [/usr/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 3.0.3 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
https://aka.ms/dotnet-download

Visual Studio Code Extensions

Extension	Author	Version
calculator	lixquid	0.1.1
csharp	ms-dotnettools	1.21.15
docomment	k--kato	0.1.8
mono-debug	ms-vscode	0.15.8
template	yongwoo	1.1.5
vscode-csharp-snippets	jorgeserrano	0.3.1