Generate the extension list from data

[sampsyo]

Currently, the list of extensions in the manual is hard-coded in a JavaScript file, like this:

riscv.fyi/src/lib/loadExtensions.ts

Lines 5 to 10 in d24668c

	const descriptions = {
	I: "Base Integer",
	E: "Embedded Base",
	M: "Integer Multiply/Divide",
	A: "Atomic Instructions",
	F: "Single-Precision Floating Point",

We should instead get the list of extensions directly from the RISC-V Unified Database data that we are depending on.

I am not sure whether the UDB data has short descriptions of each extension as we currently have in the hard-coded JS. If not, then I think we should provide those ourselves in a "file on the side," i.e., a JSON file whose sole purpose is to list those English-language descriptions. But even so, the canonical list of all extensions should come from UDB, not from this file on the side.