Fix Unit Test debugging in October VS Code

[gregg-miskelly]

The VS Code team is removing support for the vscode.startDebug command that this extension uses.

Here is where we use it:

PS C:\dd\omnisharp-vscode> f /s startDebug *.ts
src\features\dotnetTest.ts:285:            .then(config => vscode.commands.executeCommand('vscode.startDebug', config))
src\omnisharp\server.ts:291:                    if (commands.find(c => c === 'vscode.startDebug')) {

VS Code release notes: https://code.visualstudio.com/updates/v1_17#_debug-api-updates
Related issues: microsoft/vscode#33791, microsoft/vscode#33795

[gregg-miskelly]

The new debugging API was introduced in the August release (that shipped in early September) and the old API will be removed in the October release (which ships in early November).

[gregg-miskelly]

The new APIs were added in the 1.15 (July) release: https://code.visualstudio.com/updates/v1_15