Add missing definitions for text processing standard libraries (pp, shellwords, strscan)

[zonuexe]

Add missing methods, classes, and constants for pp, shellwords, and strscan.

Note: abbrev, base64, and nkf have been excluded as they are in ALUMNI_STDLIBS and planned to be removed from the rbs repo.

Changes

Ruby Method	Change	C function
PP#pp_hash_pair	Add method pp_hash_pair returning void	https://github.com/ruby/pp/blob/master/lib/pp.rb
PP::VERSION	Add constant VERSION	https://github.com/ruby/pp/blob/master/lib/pp.rb
Shellwords::VERSION	Add constant VERSION	https://github.com/ruby/shellwords/blob/master/lib/shellwords.rb
StringScanner::Error	Add exception class inheriting StandardError	https://github.com/ruby/strscan/blob/master/ext/strscan/strscan.c

[ksss]

abbrev, base64, and nkf are planned to be removed from the rbs repo.
Please submit your requests to each gem.

rbs/lib/rbs/collection/config/lockfile_generator.rb

Lines 7 to 22 in 5a8d8ac

	ALUMNI_STDLIBS = {
	"mutex_m" => ">= 0.3.0",
	"abbrev" => nil,
	"base64" => nil,
	"benchmark" => nil,
	"bigdecimal" => nil,
	"csv" => nil,
	"kconv" => nil,
	"logger" => nil,
	"minitest" => nil,
	"net-smtp" => nil,
	"nkf" => nil,
	"observer" => nil,
	"cgi" => nil,
	"pstore" => nil,
	}

[zonuexe]

Thank you for pointing this out! I have excluded abbrev, base64, and nkf from this PR, keeping only pp, shellwords, and strscan. I will submit separate PRs to each gem repository.
Also updated constant assertions in test files to use assert_const_type.