Tag helpers and Razor expressions don't work well together on the same line

[CristianVladescu]

Describe the bug

Tag helpers and Razor expressions don't work well together on the same line.
Take for instance this line of code:
<button @(group.Builtin ? "disabled" : "") asp-page-handler="ShowGroupModal" type="submit">Edit</button>

In this case the asp-page-handler TagHelper has no effect.
If I swap the order, everything works, but Visual Studio does not recognize the expression syntax.

.NET Core SDK (reflecting any global.json):
 Version:   2.1.502
 Commit:    c74ce8f29f

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17134
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.1.502\

Host (useful for support):
  Version: 2.1.6
  Commit:  3f4f8eebd8

.NET Core SDKs installed:
  2.1.403 [C:\Program Files\dotnet\sdk]
  2.1.500 [C:\Program Files\dotnet\sdk]
  2.1.502 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

Version 15.9.4
VisualStudio.15.Release/15.9.4+28307.222
Microsoft .NET Framework
Version 4.7.03056

Installed Version: Community

Application Insights Tools for Visual Studio Package   8.14.11009.1
Application Insights Tools for Visual Studio

ASP.NET and Web Tools 2017   15.9.04012.0
ASP.NET and Web Tools 2017

ASP.NET Core Razor Language Services   15.8.31590
Provides languages services for ASP.NET Core Razor.

ASP.NET Web Frameworks and Tools 2017   5.2.60913.0
For additional information, visit https://www.asp.net/

Azure App Service Tools v3.0.0   15.9.03024.0
Azure App Service Tools v3.0.0

Azure Data Lake Node   1.0
This package contains the Data Lake integration nodes for Server Explorer.

Azure Data Lake Tools for Visual Studio   2.3.3000.2
Microsoft Azure Data Lake Tools for Visual Studio

Azure Functions and Web Jobs Tools   15.9.02046.0
Azure Functions and Web Jobs Tools

Azure Stream Analytics Tools for Visual Studio   2.3.3000.2
Microsoft Azure Stream Analytics Tools for Visual Studio

C# Tools   2.10.0-beta2-63501-03+b9fb1610c87cccc8ceb74a770dba261a58e39c4a
C# components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Common Azure Tools   1.10
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.

JavaScript Language Service   2.0
JavaScript Language Service

JavaScript Project System   2.0
JavaScript Project System

Microsoft Azure HDInsight Azure Node   2.3.3000.2
HDInsight Node under Azure Node

Microsoft Azure Hive Query Language Service   2.3.3000.2
Language service for Hive query

Microsoft Azure Stream Analytics Language Service   2.3.3000.2
Language service for Azure Stream Analytics

Microsoft Azure Stream Analytics Node   1.0
Azure Stream Analytics Node under Azure Node

Microsoft Azure Tools   2.9
Microsoft Azure Tools for Microsoft Visual Studio 2017 - v2.9.10730.2

Microsoft Continuous Delivery Tools for Visual Studio   0.4
Simplifying the configuration of Azure DevOps pipelines from within the Visual Studio IDE.

Microsoft JVM Debugger   1.0
Provides support for connecting the Visual Studio debugger to JDWP compatible Java Virtual Machines

Microsoft Library Manager   1.0
Install client-side libraries easily to any web project

Microsoft MI-Based Debugger   1.0
Provides support for connecting Visual Studio to MI compatible debuggers

Microsoft Visual Studio Tools for Containers   1.1
Develop, run, validate your ASP.NET Core applications in the target environment. F5 your application directly into a container with debugging, or CTRL + F5 to edit & refresh your app without having to rebuild the container.

Node.js Tools   1.4.21001.1 Commit Hash:8dd15923800d931b153ab9e4de74e42a74eba5e6
Adds support for developing and debugging Node.js apps in Visual Studio

NuGet Package Manager   4.6.0
NuGet Package Manager in Visual Studio. For more information about NuGet, visit http://docs.nuget.org/.

ProjectServicesPackage Extension   1.0
ProjectServicesPackage Visual Studio Extension Detailed Info

ResourcePackage Extension   1.0
ResourcePackage Visual Studio Extension Detailed Info

ResourcePackage Extension   1.0
ResourcePackage Visual Studio Extension Detailed Info

SQL Server Data Tools   15.1.61810.11040
Microsoft SQL Server Data Tools

ToolWindowHostedEditor   1.0
Hosting json editor into a tool window

TypeScript Tools   15.9.20918.2001
TypeScript Tools for Microsoft Visual Studio

Visual Basic Tools   2.10.0-beta2-63501-03+b9fb1610c87cccc8ceb74a770dba261a58e39c4a
Visual Basic components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used.

Visual F# Tools 10.2 for F# 4.5   15.8.0.0.  Commit Hash: 6e26c5bacc8c4201e962f5bdde0a177f82f88691.
Microsoft Visual F# Tools 10.2 for F# 4.5

Visual Studio Code Debug Adapter Host Package   1.0
Interop layer for hosting Visual Studio Code debug adapters in Visual Studio

Visual Studio Tools for Containers   1.0
Visual Studio Tools for Containers