Is there any way to create a dashed line within Premiere Pro- say in the title tool or otherwise, without having to import from external sources?
A possible workaround would be to use the Venetian Blinds filter. Here with a bit of experimentation I've made a path with a stroke of 20 and for the blind effect I have doubled the width to 40.
The Transition Completion value is set to 50% so that half of the effect is achieved. You might want to play around with the settings if you want longer dashes or gaps.
This effect is typically used as a transition, but as we have not used keyframes for the transition there will be no animation. This effect only works with straight lines, if the line is at an angle, you will need to adjust the Direction value.
You may find it more appropriate to design dashed lines in After Effects as there are options for stroke gap and width to easily create a dashed line.