prop_data.3: fix typo

Improvements to the problib(3) API:

==> Provide a much more complete set of setters and getters for different
value types in the prop_array_util(3) and prop_dictionary_util(3)
functions.

==> Overhaul the prop_data(3), prop_number(3), and prop_string(3) APIs
to be easier to use and less awkwardly named, Deprecate the old
awkward names, and produce link-time warnings when they are referenced.

==> Deprecate mutable prop_data(3) and prop_string(3) objects. The old
APIs that support them still exist, but will now produce link-time
warnings when used.

==> When the new prop_string(3) API is used, strings are internally
de-duplicated as a memory footprint optimization.

==> Provide a rich set of bounds-checked gettter functions in and a
corresponding set of convenience setters in the prop_number(3) API.

==> Add a new prop_bool_value(3) function that is equivalent to
prop_bool_true(3), but aligned with the new "value" routines in
prop_data(3), prop_string(3), and prop_number(3).

branches: 1.8.12;
Use .Fn to refer a function name instead of Nm.
Also, use Xr to refer problib(3) in the HISTORY section instead of Nm.

While parsing the man pages, any .Nm occurrence gets replaced by the
value specified in the NAME section. Referencing individual function
names with .Nm was causing makemandb(8) to replicate the complete
NAME section for every such occurrence. This was leading to an
ugly looking snippet in apropos(1)'s output when searched for
any of these man pages.

branches: 1.7.30; 1.7.34;
Fix some ordering inconsistencies, noted by Silas Silva in PR 42415.

Convert TNF licenses to new 2 clause variant

branches: 1.5.4;
PR/37838: Stathis Kamperis: proplib documentation enhancements

branches: 1.4.2;
boolean_t -> bool
TRUE -> true
FALSE -> false

Add prop_data_size() to SYNOPSIS.

branches: 1.2.6; 1.2.10;
Drop trailing whitespace.

Initial commit of proplib, a library for manipulating property lists and
converting to/from an XML external representation (based on Apple XML
property lists). Works in the kernel and user space.