Keymap: Add a method to get modified characters for a key

This method fills out the passed-in BList of modified utf-8 characters for
a given utf-8 character and set of modifiers.

For example if you pass in "=" and B_SHIFT_KEY the list will get filled
out with each character in the shift map that has "=" in the normal map.

Each supported keymap modifier combination is available.

The reason this is useful will soon become apparent.

A BList is used because the character might be mapped multiple times,
for example if you have a Mac keyboard you've got two "=" keys, one in
0x1d and one in 0x6a.

The caller is responsible for creating the BList and destroying it as well as
freeing the resulting character strings.

headers/private/shared/Keymap.h

@@ -14,6 +14,8 @@
 #include <InterfaceDefs.h>
 
 
+class BList;
+
 class BKeymap {
 public:
 								BKeymap();
@@ -38,6 +40,9 @@ public:
 			void				GetChars(uint32 keyCode, uint32 modifiers,
 									uint8 activeDeadKey, char** chars,
 									int32* numBytes) const;
+			status_t			GetModifiedCharacters(const char* normal,
+									int32 modifiers,
+									BList* _modifiedCharacters);
 
 			const key_map&		Map() const { return fKeys; }