[FEATURE] Perform case-insensitive sorting

[thomasrawiel]

It's currently not possible to sort results on a case-insensitive basis.

Given the following example: "Sort by page title" - but could be anything really, like extbase record title, news title or similar things.
For example a list of brands, company names, movie titles or similar that can start with lowercase letters or numbers

Indexing the record title

plugin.tx_solr.index.queue.pages.fields {
   pageTitle_stringS = title
}

In the result query sort by the indexed title field

query {
  sortBy = pageTitle_stringS ASC
  filter {
    types = type:pages
    #types = type:tx_myext_domain_model_something
  }
}

results in a correctly sorted list, except that lowercase titles are sorted after uppercase titles.
For example
expecting A, a, B, b, C, c, D, d, E, F
but is sorted A, B, C, D, E, F, a, b, c, d

Describe the solution you'd like
Possible solution https://dev.to/cendekia/perform-case-insensitive-sorting-in-solr-6k4

Maybe add an option to switch between case-sensitive and case-insensitive

query {
  sortBy = pageTitle_stringS ASC
  sortByIgnoreCase = 0 #disables case-insensitive sorting
  sortByIgnoreCase = 1 #enables case-insensitive sorting

  filter {
    types = type:pages
  }
}

In my opinion case-insensitive sorting should be the default.

Describe alternatives you've considered
Currently solved by indexing the title field in lowercase:

plugin.tx_solr.index.queue.pages.fields {
   pageTitle_stringS = title

   sortPageTitle_stringS = TEXT
   sortPageTitle_stringS.field = title
   sortPageTitle_stringS.stdWrap.case = lower
}

...

query {
  sortBy = sortPageTitle_stringS ASC
  filter {
    types = type:pages
  }
}