Multiline errors support

[9il]

Example:

source/mir/ndslice/dynamic.d(419,27): Error: CTFE failed because of previous errors in isPermutation
source/mir/ndslice/dynamic.d(419,9):        while evaluating: static assert([3LU, 0LU, 1LU, 2LU].isPermutation)

[LaurentTreguier]

Right now it looks like it's not possible to accumulate line messages. VSCode's multiline problem matching allows taking information across multiple lines, but only the first filename, the first error message etc. will be used. This could be a new feature to add to VSCode