[CodeGen] Tweak whitespace in LiveInterval printing

When printing a LiveInterval, tweak the use of single and double spaces
to try to make it clearer that the valnos are associated with the
preceding range or subrange, not the following subrange.

Compare the output before and then after this patch:
%1 [32r,144r:0)  0@32r L000000000000000C [32r,144r:0)  0@32r L00000000000000F3 [32r,32d:0)  0@32r weight:0.000000e+00
%1 [32r,144r:0) 0@32r  L000000000000000C [32r,144r:0) 0@32r  L00000000000000F3 [32r,32d:0) 0@32r  weight:0.000000e+00

Differential Revision: https://reviews.llvm.org/D113671