Fix WriteAsOperand to not emit a leading space character. Adjust

Fix WriteAsOperand to not emit a leading space character. Adjust
its callers to emit a space character before calling it when a
space is needed.

This fixes several spurious whitespace issues in
ScalarEvolution's debug dumps. See the test changes for
examples.

This also fixes odd space-after-tab indentation in the output
for switch statements, and changes calls from being printed like
this:
  call void @foo( i32 %x )
to this:
  call void @foo(i32 %x)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56196 91177308-0d34-0410-b5e6-96231b3b80d8