Added support for scoped function calltips

[krogank9]

I created function read_scope_prefix which is similar to read_current_word. It gets the scope of the word the cursor is on:

if the user types: ScopeA::ScopeB::Function
it will return ScopeA::ScopeB

Then I used my read_scope_prefix function in editor_show_calltip where find_calltips is called. To find_calltips I added an argument const gchar *scope to send the value over. Then, inside find_calltips the function tm_workspace_find (which then calls fill_find_tags_array) is called. tm_workspace_find & fill_find_tags_array already had a scope argument that was unused, so I just passed in the scope argument.

However, in fill_find_tags_array, when passed a non-null scope it filters any tags that are not exactly equal to that scope. E.g. if you have ClassA { setterFunc(abc) {} } ClassA::setterFunc will work but then ClassA obj.setterFunc will no longer work because scope != NULL. So I added a check inside fill_find_tags_array. First, it loops through the list of tags and attempts to find an exact match for the scope being typed, if it doesn't find a match, the function will just ignore the scope as if it had been set to NULL from the start.

[elextr]

It doesn't read the "current" scope, which is a lexical attribute of the position in the code, rather it reads scope related prefixes that exist in the text.

So I suggest renaming it to read_scope_prefix.