ref(core): rename gen_ai.request.messages to gen_ai.input.messages

[nicohrubec]

• rename gen_ai.request.messages to gen_ai.input.messages
• also rename gen_ai.request.messages.original_length to gen_ai.input.messages.original_length (not sure if we get rid of this attribute in favor of sentry.sdk_meta.gen_ai.input.messages.original_length but for now renaming to this so we stay consistent since I will do the other rename in a separate PR)
• fix some more test constants I missed with the last PR

Closes #18919

[github-actions]

node-overhead report 🧳

Note: This is a synthetic benchmark with a minimal express app and does not necessarily reflect the real-world performance impact in an application.

Scenario	Requests/s	% of Baseline	Prev. Requests/s	Change %
GET Baseline	8,973	-	8,986	-0%
GET With Sentry	1,710	19%	1,660	+3%
GET With Sentry (error only)	6,055	67%	6,067	-0%
POST Baseline	1,205	-	1,194	+1%
POST With Sentry	573	48%	595	-4%
POST With Sentry (error only)	1,048	87%	1,049	-0%
MYSQL Baseline	3,291	-	3,291	-
MYSQL With Sentry	487	15%	444	+10%
MYSQL With Sentry (error only)	2,688	82%	2,671	+1%

View base workflow run

[RulaKhaled]

Very nice