Rename internal is_ascii_char to is_ascii_alphabet_char

[aaronfranke]

static _FORCE_INLINE_ bool is_ascii_alphabet_char(char32_t c) {
	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}

Reasoning: This is the non-numeric version of is_ascii_alphanumeric_char. is_ascii_char can be misleading because it could imply all ASCII characters, including numbers, symbols, and control characters. Since this method explicitly only checks for alphabetical characters, it should be called is_ascii_alphabet_char (or similar).

[akien-mga]

Thanks!