Zero-width spaces in spec html

[svenvh]

Various function names in the spec have zero-width spaces in them, e.g. get_​sub_​group_​size. It seems this was done deliberately in #950 :

+// Note: the Unicode "zero width space" (​) is used in some places to
+// cause long function names to break much more sensibly.

The zero-width spaces end up in the rendered html, which interferes with copy/pasting a function name from the html:

• Searches for that copied function name will not match actual occurrences of that function name in for example source code files.
• Pasting the copied function name into a source file includes the zero-width spaces, which will need to be removed.

[bashbaug]

I'll fix this - this was something I did a long time ago as part of the "extended subgroups" extension spec, probably before we observed that using the unicode "zero width spaces" in the HTML specs has some problems (see #393),