Switch the CharSourceRange array to a small vector. The array was

a stack array of a magical size with an assert() that we never
overflowed it. That seems incredibly risky. We also have a very nice API
for bundling up a vector we expect to usually have a small size without
loss of functionality or security if the size is excessive.

The fallout is to remove the last pointer+size parameter pair that are
traced through the recursive caret diagnostic emission.

llvm-svn: 139217