(GH-10798) Clarify how to find exception names in about_Trap (#10803)

* (MAINT) Fixup grammar & formatting for about_Trap

This change addresses issues raised against the `about_Trap` topic by
Vale, Acrolinx, and the PowerShell docs style guide.

It cleans up the prose, fixes grammar, and standardizes code formatting.

* (GH-10798) Clarify how to find exception names in about_Trap

Prior to this change, the `about_Trap` topic explained how to
use specific exceptions with a `trap` statement, but not how
to discover the exception names for that purpose.

This change:

- Adds prose and example to the section "Trapping specific errors"
  that covers how to get the full name of an exception
- Resolves #10798
- Fixes AB#200723