Pad RISC-V RVC instructions like Thumb2

[fuad1502]

We're introducing RVC instructions to RISC-V JIT in dotnet/runtime: dotnet/runtime#117408

With that PR and this PR, output of R2RDump tool for the following C# method:

public static long FunAdd(long a, long b)
{
        return a + b;
}

is as follows:

long Program.FunAdd(long, long)
Handle: 0x06000002
Rid: 2
EntryPointRuntimeFunctionId: 1
Number of RuntimeFunctions: 1

long Program.FunAdd(long, long)
Id: 1
StartAddress: 0x00010BD0
Size: 34 bytes
UnwindRVA: 0x0001091C

Debug Info
    Bounds:
    Native Offset: 0x0, Prolog, Source Types: StackEmpty
    Native Offset: 0x10, IL Offset: 0x0000, Source Types: StackEmpty
    Native Offset: 0x12, Epilog, Source Types: StackEmpty

    Variable Locations:
    Variable Number: 0
    Start Offset: 0x0
    End Offset: 0x10
    Loc Type: VLT_REG
    Register: A0

    Variable Number: 1
    Start Offset: 0x0
    End Offset: 0x10
    Loc Type: VLT_REG
    Register: A1

10bd0: 13 01 01 ff     addi    sp, sp, -16
10bd4: 23 30 81 00     sd      s0, 0(sp)
10bd8: 23 34 11 00     sd      ra, 8(sp)
10bdc: 13 04 01 00     mv      s0, sp
10be0: 2e 95           add     a0, a0, a1 ;; RVC instruction
10be2: 83 30 81 00     ld      ra, 8(sp)
10be6: 03 34 01 00     ld      s0, 0(sp)
10bea: 13 01 01 01     addi    sp, sp, 16
10bee: 67 80 00 00     ret

[fuad1502]

Hi @am11 can you help me review this PR or assign an appropriate reviewer with write access for this PR? 🙏 The related PR in dotnet/runtime (dotnet/runtime#117408) is already merged in 👍

[am11]

@jakobbotsch, @EgorBo, PTAL. LGTM! :)