Move SamplerParams clamping logic to AIManager

The AIManager::CreateLanguageModel() mojo interface will clamp or set
default values for arbitrary SamplerParams received from the caller.
This CL moves this logic to AIManager - when processing the mojo
message - so that its callees can assume these params are valid

Change-Id: Ic97f0da6dfb78840eb2d77e7bc1b6d4c04afb5f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6338769
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Auto-Submit: Austin Sullivan <asully@chromium.org>
Reviewed-by: Clark DuVall <cduvall@chromium.org>
Commit-Queue: Austin Sullivan <asully@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1430461}