Further fixed (in branch text-elided) 'text see' with indices in elided lines, since previous fixes such as [5f352f3a71] were not correct in all cases.

Now ALL calls to CalculateDisplayLineHeight use an index that is at the start of a display line, as requested by CalculateDisplayLineHeight.

Test case 'L':
--------------
package require Tk
pack [text .t]
pack configure .t -expand 1 -fill both
for {set i 1} {$i < 50} {incr i} {
    .t insert end "Line $i\n"
}
# button just for having a line with a larger height
button .t.b -text "Test" -bd 2 -highlightthickness 2
.t window create 21.0 -window .t.b
wm geometry . 300x200+0+0
.t tag add hidden 15.36 21.0
.t tag configure hidden -elide true
# Indices 21.0, 17.0 and 15.0 are all on the same display line
# therefore index @0,0 shall be the same for all of them
.t see end
update
.t see 21.0
update
set ind1 [.t index @0,0]
.t see end
update
.t see 17.0
update
set ind2 [.t index @0,0]
.t see end
update
.t see 15.0
update
set ind3 [.t index @0,0]
list [expr {$ind1 == $ind2}] [expr {$ind1 == $ind3}] ; correct is {1 1}