Update tuple tests, and merge in expr-category

[jonmeow]

In the vein of https://github.com/carbon-language/carbon-lang/pull/5455. This is based on #5546 for the int prelude, and also adds negate for testing.

This merges the one expr_category test into tuple testing because it seemed closely associated (particularly with in_place_tuple_init.carbon), and it didn't seem worth keeping a directory for a single test.

Note the entire "access" directory is combined into element_access.carbon.