Bring Lua to 5.4.6. (#1214)

This essentially re-does the work of #875 on top of master.

This is what I did to check that Cosmo's Lua extensions still worked:

```
$ build/bootstrap/make MODE=aarch64 o/aarch64/third_party/lua/lua
$ ape o/aarch64/third_party/lua/lua
>: 10
10
>: 010
8
>: 0b10
2
>: string.byte("\e")
27
>: "Hello, %s" % {"world"}
Hello, world
>: "*" * 3
***
```

`luaL_traceback2` was used to show the stack trace with parameter
values; it's used in `LuaCallWithTrace`, which is used in Redbean to run
Lua code. You should be able to see the extended stack trace by running
something like this: `redbean -e "function a(b)c()end a(2)"` (with
"params" indicating the extended stack trace):

```
stack traceback:
 [string "function a(b)c()end a(2)"]:1: in function 'a', params: b = 2;
 [string "function a(b)c()end a(2)"]:1: in main chunk
```
@pkulchenko confirmed that I get the expected result with the updated
code.

This is what I did to check that Lua itself still worked:

```
$ cd third_party/lua/test/
$ ape ../../../o/aarch64/third_party/lua/lua all.lua
```

There's one test failure, in `files.lua`:

```
***** FILE 'files.lua'*****
testing i/o
../../../o/aarch64/third_party/lua/lua: files.lua:84: assertion failed!
stack traceback:
[C]: in function 'assert'
files.lua:84: in main chunk
(...tail calls...)
all.lua:195: in main chunk
[C]: in ?
.>>> closing state <<<
```

That isn't a result of these changes; the same test is failing in
master.

The failure is here:

```lua
if not _port then   -- invalid seek
  local status, msg, code = io.stdin:seek("set", 1000)
  assert(not status and type(msg) == "string" and type(code) == "number")
end
```

The test expects a seek to offset 1,000 on stdin to fail — but it
doesn't. `status` ends up being the new offset rather than `nil`.

If I comment out that one test, the remaining tests succeed.

third_party/lua/test/verybig.lua

@@ -52,7 +52,7 @@ if _soft then return 10 end
 print "testing large programs (>64k)"
 
 -- template to create a very big test file
-prog = [[$
+local prog = [[$
 
 local a,b
 
@@ -85,7 +85,7 @@ function b:xxx (a,b) return a+b end
 assert(b:xxx(10, 12) == 22)   -- pushself with non-constant index
 b["xxx"] = undef
 
-s = 0; n=0
+local s = 0; local n=0
 for a,b in pairs(b) do s=s+b; n=n+1 end
 -- with 32-bit floats, exact value of 's' depends on summation order
 assert(81800000.0 < s and s < 81860000 and n == 70001)
@@ -93,7 +93,7 @@ assert(81800000.0 < s and s < 81860000 and n == 70001)
 a = nil; b = nil
 print'+'
 
-function f(x) b=x end
+local function f(x) b=x end
 
 a = f{$3$} or 10
 
@@ -118,7 +118,7 @@ local function sig (x)
   return (x % 2 == 0) and '' or '-'
 end
 
-F = {
+local F = {
 function ()   -- $1$
   for i=10,50009 do
     io.write('a', i, ' = ', sig(i), 5+((i-10)/2), ',\n')
@@ -138,14 +138,14 @@ function ()   -- $3$
 end,
 }
 
-file = os.tmpname()
+local file = os.tmpname()
 io.output(file)
 for s in string.gmatch(prog, "$([^$]+)") do
   local n = tonumber(s)
   if not n then io.write(s) else F[n]() end
 end
 io.close()
-result = dofile(file)
+local result = dofile(file)
 assert(os.remove(file))
 print'OK'
 return result