Derive SYMBOL-LOOKUP intern name via symbol-name

[genworks]

This way, lookups will work under lowercase readtable-case.

coloring-types.lisp resolves the per-language lookup functions at
runtime via (intern "SYMBOL-LOOKUP" :clhs-lookup) (likewise
:r5rs-lookup, :elisp-lookup, :cocoa-lookup — four sites). The
runtime intern is clearly deliberate, since the lookup packages are
optional and find-package-guarded — but the hardcoded uppercase
string isn't case-portable. String literals don't follow
readtable-case, while definition names do: on an implementation
whose symbols read lowercase (e.g. modern-mode Allegro CL, where
readtable-case is :preserve over lowercase standard symbols),
(defun symbol-lookup ...) interns "symbol-lookup", and the
uppercase string-intern creates a distinct, unfbound symbol. The
result is an undefined-function error whenever a Lisp code block is
colorized.

This patch derives the name the same way the definition's name was
derived — (intern (symbol-name '#:symbol-lookup) :clhs-lookup) —
so it matches under any readtable-case.

On a conforming :upcase implementation this is provably a no-op.
On stock SBCL:

(string= (symbol-name '#:symbol-lookup) "SYMBOL-LOOKUP")  ; => T
(eq (intern (symbol-name '#:symbol-lookup) :clhs-lookup)
    (intern "SYMBOL-LOOKUP" :clhs-lookup))                 ; => T

Under modern-mode Allegro CL, (symbol-name '#:symbol-lookup) yields
"symbol-lookup", matching the actual definitions — verified there:
the patched form resolves to the genuine fbound symbol-lookup,
where the hardcoded string previously landed on an unbound symbol.

(No pure-SBCL failing testcase is possible for this one via readtable
tricks: under readtable-case :invert the lowercase defun names
invert to "SYMBOL-LOOKUP" and match the hardcoded string. The
string literal's immunity to readtable-case is exactly the bug.)