Made the ttk::treeview cell padding scaling-aware. #3341

Job	Run time
build (gcc)	1m 41s
build (gcc, CFLAGS=-DTK_NO_DEPRECATED=1)	1m 43s
build (gcc, --disable-shared)	1m 45s
build (gcc, --disable-xft)	1m 49s
build (gcc, --disable-xss)	1m 41s
build (gcc, --enable-symbols)	1m 26s
build (clang)	2m 1s
build (clang, CFLAGS=-DTK_NO_DEPRECATED=1)	2m 0s
build (clang, --disable-shared)	1m 53s
build (clang, --disable-xft)	2m 5s
build (clang, --disable-xss)	2m 4s
build (clang, --enable-symbols)	1m 32s
test (gcc)	4m 19s
test (gcc, --disable-xft)	4m 4s
test (gcc, --enable-symbols)	3m 28s
	33m 31s

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