asm: complete arm64 instruction encodings for homemade assembler (#431)

This commit implements all the arm64 instruction encodings necessary
for our JIT compiler and replaces the golang-asm assembler with our
handmade assembler on arm64 platform. Notably, this allows us to do
concurrent compilations.

This closes #233 combined with #406.

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>
Co-authored-by: Adrian Cole <adrian@tetrate.io>

internal/u64/u64.go

@@ -1,6 +1,6 @@
 package u64
 
-// LeBytes returns a byte array corresponding to the 8 bytes in the uint64 in little-endian byte order.
+// LeBytes returns a byte slice corresponding to the 8 bytes in the uint64 in little-endian byte order.
 func LeBytes(v uint64) []byte {
 	return []byte{
 		byte(v),