[libc][z/OS] Remove ASCII trick to fix EBDIC std::from_char (#116078)

This PR will fix the following lit in all EBCDIC variations on z/OS: `std/utilities/charconv/charconv.from.chars/floating_point.pass.cpp` The trick to test for `e` and `E` is working only in ASCII. The fix is to simply test for both lower and upper case exponent letter `e` and `E` respectfully.

Author: zibi2

libc/src/__support/high_precision_decimal.h

@@ -350,7 +350,8 @@ class HighPrecisionDecimal {
  if (!saw_dot)
  this->decimal_point = total_digits;
 
- if (num_cur < num_len && ((num_string[num_cur] | 32) == 'e')) {
+ if (num_cur < num_len &&
+ (num_string[num_cur] == 'e' || num_string[num_cur] == 'E')) {
  ++num_cur;
  if (isdigit(num_string[num_cur]) || num_string[num_cur] == '+' ||
  num_string[num_cur] == '-') {