[epics-msi-substitution] does not accept special characters without quotes

[vnadot]

List of characters not accepted by tree-sitter-epics but works in IOC (in my case for EGU field:

• µ for µA
• ° for °C
• % for percentage

Please note that if I put these specials characters inside quotes, tree-sitter-epics is happy.

file "x.template"
{
  pattern
  { SIGNAL,         EGU}
  { MY_PREFIX,  µA }
}

file "x.template"
{
  pattern
  { SIGNAL,         EGU}
  { MY_PREFIX,  °C }
}

file "x.template"
{
  pattern
  { SIGNAL,        EGU}
  { MY_PREFIX,  % }
}