The patch for "MDEV-25440: Indexed CHAR ... broken with NO_PAD collations"
fixed these scenarios from MDEV-26743:
- Basic latin letter vs equal accented letter
- Two letters vs equal (but space padded) expansion

However, this scenario was still broken:
- Basic latin letter (but followed by an ignorable character)
  vs equal accented letter

Fix:
When processing for a NOPAD collation a string with trailing ignorable
characters, like:
  '<non-ignorable><ignorable><ignorable>'

the string gets virtually converted to:
  '<non-ignorable><ignorable><ignorable><space><space><space>...'

After the fix the code works differently in these two cases:
1. <space> fits into the "nchars" limit
2. <space> does not fit into the "nchars" limit

Details:

1. If "nchars" is large enough (4+ in this example),
   return weights as follows:

  '[weight-for-non-ignorable, 1 char] [weight-for-space-character, 3 chars]'

  i.e. the weight for the virtual trailing space character now indicates
  that it corresponds to total 3 characters:
  - two ignorable characters
  - one virtual trailing space character

2. If "nchars" is small (3), then the virtual trailing space character
   does not fit into the "nchar" limit, so return 0x00 as weight, e.g.:

  '[weight-for-non-ignorable, 1 char] [0x00, 2 chars]'

Adding corresponding MTR tests and unit tests.