bug#48281: buffer_local_value and find_symbol_value duplicate functionality

[Spencer Baugh]

find_symbol_value is described as:

  Find the value of a symbol, returning Qunbound if it's not bound.

buffer_local_value does the same, except that it allows one to specify a
buffer.

Yet they both implement symbol lookup, without sharing code.  And given
that the comment above find_symbol_value says "Great care is required
for this.", I'm guessing that one or both of them may have bugs that the
other does not.  Especially because buffer_local_value is simpler than
find_symbol_value, despite doing an ostensibly more complicated job...

How about unifying them into a single function?  Would a patch doing
that be accepted?

Alternatively, maybe I'm missing some detail about why they're
different?