Sync string_gf.c with pokeplatinum and pokeheartgold

[AsparagusEduardo]

Matching PRs:

• pokeplatinum: Sync string_gf.c with pokediamond and pokeheartgold pokeplatinum#875
• pokeheartgold: Sync string_gf.c with pokediamond and pokeplatinum pokeheartgold#432

Notes:

• Name changes compared to the left or right sides are signaled using an * for easier visibility.
• In the right column, if there's a /, it indicates that the pokediamond name is different from the pokeheartgold.
• If there's a (n/a) it means that the symbol doesn't exist in the corresponding side.
• If there's a (new), it means that the constant wasn't present in the corresponding side and it will be added with the new synced name.

List of renames:

pokeplatinum                    | PR                            | pokeheartgold / pokediamond
                                |                               |
 include/string_gf.h            | include/string_gf.h           | *include/pm_string.h / *include/string16.h
 src/string_gf.c                | (arm9/)src/string_gf.c        | src/pm_string.c / *arm9/src/unk_02021934.c
                                
 String_Free                    | String_Free                   | *String_Delete
*String_Init                    | String_New                    |  String_New
 String_Copy                    | String_Copy                   |  String_Copy / *StringCopy
 String_Clone                   | String_Clone                  | *String_Dup / *StringDup
*String_NumLines                | String_CountLines             |  String_CountLines / *StringCountLines
*String_CopyLineNum             | String_CopyLine               | *String_GetLineN / *StringGetLineN
*String_Length                  | String_GetLength              |  String_GetLength / *StringGetLength
 String_Clear                   | String_Clear                  | *String_SetEmpty
 String_FormatInt               | String_FormatInt              | *String16_FormatInteger
 String_FormatU64               | String_FormatU64              | *String16_FormatUnsignedLongLong / (n/a)
 String_Concat                  | String_Concat                 | *String_Cat / *StringCat
 String_ConcatTrainerName       | String_ConcatTrainerName      | *String_Cat_HandleTrainerName / *StringCat_HandleTrainerName
*String_ToChars                 | String_CopyToChars            | *CopyStringToU16Array
*String_CopyChars               | String_CopyFromChars          | *CopyU16ArrayToString
 String_CopyNumChars            | String_CopyNumChars           | *CopyU16ArrayToStringN
 (n/a)                          | String_AddRadioStatic         | *String_RadioAddStatic / (n/a)
 String_AtoI                    | String_AtoI                   | *String_atoi
*String_GetData                 | String_GetChars               | *String_cstr / *String_c_str
 String_AppendChar              | String_AppendChar             | *String_AddChar / *StrAddChar
 String_UpperChar               | String_UpperChar              | *String_UpperCharN / (n/a)
 (n/a)                          | String_UpperFirstChar         |  (n/a) / *StrUpperFirstChar
                                |                               |
 enum PaddingMode               | enum PaddingMode              | *enum PrintingMode
 PADDING_MODE_NONE              | PADDING_MODE_NONE             | *PRINTING_MODE_LEFT_ALIGN
 PADDING_MODE_SPACES            | PADDING_MODE_SPACES           | *PRINTING_MODE_RIGHT_ALIGN
 PADDING_MODE_ZEROES            | PADDING_MODE_ZEROES           | *PRINTING_MODE_LEADING_ZEROS

[AsparagusEduardo]

Closing until pokeheartgold is beyond 70% decomped.