Cherry-pick invalid character stripping

Pulled from upstream:

 * [Use utilities function instead. · 4003cb5 · Islandora/islandora_solution_pack_pdf](https://github.com/Islandora/islandora_solution_pack_pdf/commit/4003cb57b5203652601fb8114f4a283b8feea346)
Use utilities function instead. · 4003cb5 · Islandora/islandora_solution_pack_pdf
 * [Add sanitation function. · be4d218 · Islandora/islandora](https://github.com/Islandora/islandora/commit/be4d218af17a12a9e21bcd6c01086ea3bf2541b5)
Add sanitation function. · be4d218 · Islandora/islandora

THIS COMMIT CAN BE DISCARDED WHEN WE UPDATE FROM 7.x-1.2

Fixes [RS: temp-davidson issues - It does not seem that full text of PDF file ingested this morning was indexed - Asana](https://app.asana.com/0/13441501451144/13445411934821)

cc: @bibliotechy Can you review code and push through to production?  Thanks!