Identified with readability-misleading-indentation.

Make the operands auto-decodable by adding `bits<0>` fields to
instructions.

Now we try to decode a vpred_n/vpred_r operand only if the instruction
being decoded has one.
We still need post-decoding pass to check/advance VPT state.

Part of #156540.

Move `DecodeT2AddrModeImm8` and `DecodeT2Imm8` definition before its
first use and eliminate the last remaining forward declarations of
decode functions.

Work on https://github.com/llvm/llvm-project/issues/156560 : Reorder ARM
disassembler decode functions to eliminate forward declarations

The operand can be decoded automatically, without the need for
post-decoding instruction modification.
Part of #156540.

This change adds basic `MCInst` verification (checks the number of
operands) and fixes detected bugs.

* `RFE*` instructions have only one operand, but `DecodeRFEInstruction`
added two.
* `DecodeMVEModImmInstruction` and `DecodeMVEVCMP` added a `vpred`
operand, but this is what `AddThumbPredicate` normally does. This
resulted in an extra `vpred` operand.
* `DecodeMVEVADCInstruction` added an extra immediate operand.
* `getARMInstruction` added a `pred` operand to instructions that don't
have one (via `DecodePredicateOperand`).
* `AddThumb1SBit` appended an extra register operand to instructions
that don't modify CPSR (such as `tBL`).
* Instructions in `NEONDup` namespace have `pred` operand that the
generated code successfully decodes. The operand was added once again by
`getARMInstruction`/`getThumbInstruction` via `AddThumbPredicate`.

Functional changes extracted from #156540.

Move all decode functions (except `DecodeT2AddrModeImm8`) that had
forward declarations around so that they are defined before their first
use and not need a forward declaration.

Work on https://github.com/llvm/llvm-project/issues/156560 : Reorder ARM
disassembler decode functions to eliminate forward declarations

Move some of the non-static-decode functions to the end of the file.
Note: moving `ARMDisassembler::AddThumbPredicate` the same way causes
the diff to be non-trivial, so not doing that here.

Move `tryAddingSymbolicOperand` and `tryAddingPcLoadReferenceComment` to
before including the generated disassembler code. This is in preparation
for rearranging the decoder functions to eliminate forward declarations.