Fix space counting for justified text

Previously, the number of stretchable spaces in a line were
miscounted, always returning one more than the actual number. We now
count them correctly.

Also, disable NBSP as an stretchable space, since in some use cases
it should not stretch and the implementation in Minikin was broken
anyway.

Test: Manual (justified text is now properly aligned on right side)
Test: bit FrameworksCoreTests:android.text.TextLineTest
Fixes: 68009059
Bug: 68204709
Change-Id: I473415a2a51eec75377d6ffc4a9adddc2033d360