Assembly.LoadFrom() cannot be debugged correctly

## Environment data
#### `dotnet --info` output:
.NET Core SDK（反映任何 global.json）:
Version: 3.0.100-preview-010184
Commit: c57bde4593

运行时环境:
OS Name: Windows
OS Version: 10.0.17763
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.0.100-preview-010184\

Host (useful for support):
Version: 3.0.0-preview-27324-5
Commit: 63a01b08e5
#### VS Code version: 1.31.1
#### C# Extension version: 1.17.1

## Steps to reproduce

When VS Code runs in debug mode to the following statement:
```csharp
Assembly assembly = Assembly.LoadFrom("Reflection.DB.MySql.dll");
```

## Expected behavior

Under normal circumstances, the program should look for "Reflection.DB.MySql.dll" in the directory where it is located
That is, the correct result is that it can be loaded into:

```
"${workspaceFolder}/02Reflection/Reflection/bin/Debug/netcoreapp3.0/Reflection.DB.MySql.dll"
```

## Actual behavior

In fact, it is looking for "Reflection.DB.MySql.dll" in the following directory:

```
"${workspaceFolder}/02Reflection/Reflection/"
```
So that the following error was finally reported:
```
'System.IO.FileNotFoundException' occurred in Reflection.dll:
Could not load file or assembly '${workspaceFolder}/02Reflection/Reflection/Reflection.DB.MySql.dll'.
```

## Project Directory Structure

```
.
│ csharp.sln
└─02Reflection
├─Reflection
│ │ Program.cs
│ │ Reflection.csproj
│ │ SimpleFactory.cs
│ └─bin
│ └─Debug
│ └─netcoreapp3.0
│ appconfig.yml
│ Microsoft.Extensions.Configuration.Abstractions.dll
│ Microsoft.Extensions.Configuration.dll
│ Microsoft.Extensions.Configuration.FileExtensions.dll
│ Microsoft.Extensions.FileProviders.Abstractions.dll
│ Microsoft.Extensions.FileProviders.Physical.dll
│ Microsoft.Extensions.FileSystemGlobbing.dll
│ Microsoft.Extensions.Primitives.dll
│ NetEscapades.Configuration.Yaml.dll
│ Reflection.DB.Interface.dll
│ Reflection.DB.Interface.pdb
│ Reflection.DB.MySql.dll
│ Reflection.DB.MySql.pdb
│ Reflection.DB.SqlServer.dll
│ Reflection.DB.SqlServer.pdb
│ Reflection.deps.json
│ Reflection.dll
│ Reflection.exe
│ Reflection.pdb
│ Reflection.runtimeconfig.dev.json
│ Reflection.runtimeconfig.json
│ System.Runtime.CompilerServices.Unsafe.dll
│ YamlDotNet.dll
│
├─Reflection.DB.Interface
│ IDBHelper.cs
│ Reflection.DB.Interface.csproj
│
├─Reflection.DB.MySql
│ MySqlHelper.cs
│ Reflection.DB.MySql.csproj
│
├─Reflection.DB.Oracle
│ OracleHelper.cs
│ Reflection.DB.Oracle.csproj
│
└─Reflection.DB.SqlServer
Reflection.DB.SqlServer.csproj
SqlServerHelper.cs
```