ts: Get discriminator lengths dynamically

[acheroncrypto]

Problem

TypeScript library uses a hardcoded value for the discriminator length in many places:

anchor/ts/packages/anchor/src/coder/borsh/discriminator.ts

Lines 1 to 4 in 293ee91

	/**
	* Number of bytes in anchor discriminators
	*/
	export const DISCRIMINATOR_SIZE = 8;

Summary of changes

• Remove the DISCRIMINATOR_SIZE constant
• Get discriminator lengths of instructions, accounts and events dynamically

---

Note: This PR is part of a greater effort explained in #3097.

[vercel]

@acheroncrypto is attempting to deploy a commit to the coral-xyz Team on Vercel.

A member of the Team first needs to authorize it.