The base64 sections were added in a time when there was no other way to
do these tests. Now we remove them again to make less "hidden" data in
the test suite.
For several test cases we instead then provide a sequence of binary
octets which is not really better, but I have tried to minimize them.
Closes#16816
The threee tags `<name>`, `</name>` and `<command>` were frequently used
with a leading space that this removes. The reason this habbit is so
widespread in testcases is probably that they have been copy and pasted.
Hence, fixing them all now might curb this practice from now on.
Closes#12028
