How does one access form controls / developer tools in LibreOffice?
First the Lo documentation is always a good starting place → Documentation/Publications. Probably the best section dealing with controls is Base but most controls work the same in Writer, Calc & so on.
Another place with many references is this post → To learn LibreOffice Base are there introductions or tutorials?. Again geared more toward Base but has important document links for items such as macros (OOME by Pitonyak) listed under
INDEPENDENT DOCUMENTATION and inspection tools under
The is probably much more but you need to be more specific as to just what you are looking for (ie: how to use a control and which control or using it in a macro).