Generate constants for script-command maps

[lhearachel]

Problem Statement

The assembler-macros used for compilation of field, battle, and trainer AI scripting use a a magic number-sequence to translate macro inputs into the byte-code understood by the game's internal script-processing engines. These numbers are processed by the engines as indices into a respective function table. This is a bit brittle, as it's easy for a modder to create a new scripting command for any engine, create an assembler-macro for the next element in the sequence, and accidentally inject their new function at the wrong place in the respective function table.

Proposal

We should generate a set of constants for use by each class of scripting's associated assembler-macros and function-tables. To illustrate, such constants would be made use of like so:

In asm/macros/scrcmd.inc:

    .macro Noop
-   .short 0
+   .short SCRCMD_NOOP
    .endm

    .macro Dummy
-   .short 1
+   .short SCRCMD_DUMMY
    .endm

    .macro End
-   .short 2
+   .short SCRCMD_END
    .endm

    .macro WaitTime frames, countdownVarID
-   .short 3
+   .short SCRCMD_WAITTIME
    .short \frames
    .short \countdownVarID
    .endm

In src/scrcmd.c:

const ScrCmdFunc Unk_020EAC58[] = {
    [SCRCMD_NOOP] = ScrCmd_Noop,
    [SCRCMD_DUMMY] = ScrCmd_Dummy,
    [SCRCMD_END] = ScrCmd_End,
    [SCRCMD_WAIT_TIME] = ScrCmd_WaitTime,
    // ommitted for brevity
};

One clear negative to this approach is that it adds some additional boilerplate for a modder when it comes to creating a new scripting command. However, there is also a clear authoritative association between macros and function-table, allowing a user to quickly jump between the two concepts without needing to sift through potentially many scripts making use of their command.