An error deep in the code of an input class shows an error message starting at the class

Using the grammar at tag https://github.com/antlr/grammars-v4/blob/distant_error_msg/swift/Swift.g4 we get a horrible error message that basically says I don't recognize the class just because he doesn't know what to do with a floating-point number, 2.0, deep in a method. Input exhibiting the problem is: https://github.com/antlr/grammars-v4/blob/master/swift/examples/Snippet.swift

I get the same error message in the interpreter and compiled code via grun, which is encouraging. ;) Somehow we need to enhance our check that looks for successfully predicted rules, rather than rolling all the way back to the class token.

Even:

```
var b = i < 2.0
```

highlights the problem in that it doesn't recognize anything but clearly parses lots of rules before it gets to the floating-point number. Here's a sample run that shows that the tokens look okay:

```
~/antlr/code/grammars-v4/swift $ grun Swift top_level -tokens
var b = i < 2.0
[@0,0:2='var',<46>,1:0]
[@1,3:3=' ',<96>,channel=1,1:3]
[@2,4:4='b',<87>,1:4]
[@3,5:5=' ',<96>,channel=1,1:5]
[@4,6:6='=',<29>,1:6]
[@5,7:7=' ',<96>,channel=1,1:7]
[@6,8:8='i',<87>,1:8]
[@7,9:9=' ',<96>,channel=1,1:9]
[@8,10:10='<',<7>,1:10]
[@9,11:11=' ',<96>,channel=1,1:11]
[@10,12:14='2.0',<93>,1:12]
[@11,15:15='\n',<96>,channel=1,1:15]
[@12,16:15='',<-1>,2:16]
line 1:12 no viable alternative at input 'var b = i < 2.0'
~/antlr/code/grammars-v4/swift $ grep "93$" *.tokens
Swift.tokens:Floating_point_literal=93
```

Reproduce the failure with Swift.g4 and examples/Snippet.swift, using grun Swift top_level with the shown floating-point input and token output. Trace how the parser reports the error after `var b = i < 2.0`; done means interpreter and compiled grun runs report the error near the offending token rather than rolling back to the class.

Written by the indexing model from the issue text.