Highlighting and diagnostics for illegal catch and catch-as clauses

[lvalkov]

The keyword as isn't being highlighted as such (instead, the variable.other scope has been applied to it).

According to the documentation, following catch may be a class name or comma-separated list of class names, therefore, anything following catch that is not the keyword as should be treated as an identifier and, if feasible, checked whether it corresponds to an actual class defined in the script. (If not, an Error diagnostic should be emitted.)

Lastly, following as must be a plain variable name (which need not be on the same line). Currently, no Error diagnostic is being emitted for that case (see last catch clause in the sample code).

try
	MsgBox('try')
catch as ErrorException
	MsgBox('catch as ErrorException')
catch MyCustomError as Exc
	MsgBox('catch MyCustomExceptionClass as Exc')
catch OSError as ; A plain variable name must follow.
	MsgBox('catch OSError as')

class MyCustomError extends Error
{
	
}

Tested with AutoHotkey_L v2.0-a137-f6f65742.