feat(docs/stdlib): split and reorder Core libraries

[novusnota]

Issue

Closes #1830.
Closes #1940 (minor fix of two descriptions)
Closes #2392
Towards #1692 (only the move from core-math to core-crypto)

This PR removes core-common and core-advanced, and distributes their contents over old and new pages, such as:

• core-send - message-sending functions, except for those in core-base
• core-crypto - moved sha256 and stuff from core-math
• core-gas - most gas-related things from core-advanced
• core-addresses - most address-related things
• core-contextstate - context and state-related things. I thought about making two disjoint pages, but those are very deeply connected things so it was better to keep them together and organize some subsections.

[novusnota]

Approves needed

UPD: I've found a way to validate links in std/internal without waiting for the weekly link check CI, hence the new commits that introduce new checks.