[REPL] 0nly do NFD normalization for latex tab-completion help if no match without it (#41870)

(cherry picked from commit ab600f8)

Author: GunnarFarneback

stdlib/REPL/src/docview.jl

@@ -403,9 +403,13 @@ function symbol_latex(s::String)
     return get(symbols_latex, s, "")
 end
 function repl_latex(io::IO, s::String)
-    # decompose NFC-normalized identifier to match tab-completion input
-    s = normalize(s, :NFD)
     latex = symbol_latex(s)
+    if isempty(latex)
+        # Decompose NFC-normalized identifier to match tab-completion
+        # input if the first search came up empty.
+        s = normalize(s, :NFD)
+        latex = symbol_latex(s)
+    end
     if !isempty(latex)
         print(io, "\"")
         printstyled(io, s, color=:cyan)

test/docs.jl

@@ -1271,6 +1271,8 @@ end
 
 # issue #36378 (\u1e8b and x\u307 are the fully composed and decomposed forms of ẋ, respectively)
 @test sprint(repl_latex, "\u1e8b") == "\"x\u307\" can be typed by x\\dot<tab>\n\n"
+# issue 39814
+@test sprint(repl_latex, "\u2209") == "\"\u2209\" can be typed by \\notin<tab>\n\n"
 
 # issue #15684
 begin