[FileCheck] Annotate input dump (3/7)

This patch implements input annotations for diagnostics that report
wrong-line matches for the directives CHECK-NEXT, CHECK-SAME, and
CHECK-EMPTY.  Instead of the usual `^~~`, which is used by later
patches for good matches, these annotations use `!~~` to mark the bad
match ranges so that this category of errors is visually distinct.
Because such matches are errors, these annotates are red when colors
are enabled.

For example:

```
$ FileCheck -dump-input=help
The following description was requested by -dump-input=help to
explain the input annotations printed by -dump-input=always and
-dump-input=fail:

  - L:     labels line number L of the input file
  - T:L    labels the only match result for a pattern of type T from line L of
           the check file
  - T:L'N  labels the Nth match result for a pattern of type T from line L of
           the check file
  - !~~    marks bad match, such as:
           - CHECK-NEXT on same line as previous match (error)
  - X~~    marks search range when no match is found, such as:
           - CHECK-NEXT not found (error)
  - ?      marks fuzzy match when no match is found
  - colors error, fuzzy match

If you are not seeing color above or in input dumps, try: -color

$ FileCheck -v -dump-input=always check2 < input2 |& sed -n '/^<<<</,$p'
<<<<<<
        1: foo bar
next:2         !~~ error: match on wrong line
>>>>>>

$ cat check2
CHECK: foo
CHECK-NEXT: bar

$ cat input2
foo bar
```

Reviewed By: george.karpenkov, probinson

Differential Revision: https://reviews.llvm.org/D53894

llvm-svn: 349420