build: move all generator scripts to src/gen/

- Move all generator Lua scripts to the `src/gen/`
- Add a `.luarc.json` to `src/gen/`
- Add a `preload.lua` to `src/gen/`
  - Add `src` to `package.path` so it aligns with `.luarc.json'
- Fix all `require` statements in `src/gen/` so they are consistent:
    - `require('scripts.foo')` -> `require('gen.foo')`
    - `require('src.nvim.options')` -> `require('nvim.options')`
    - `require('api.dispatch_deprecated')` -> `require('nvim.api.dispatch_deprecated')`

src/gen/gen_eval.lua

@@ -0,0 +1,112 @@
+local mpack = vim.mpack
+
+local autodir = arg[1]
+local metadata_file = arg[2]
+local funcs_file = arg[3]
+
+local funcsfname = autodir .. '/funcs.generated.h'
+
+--Will generate funcs.generated.h with definition of functions static const array.
+
+local hashy = require 'gen.hashy'
+
+local hashpipe = assert(io.open(funcsfname, 'wb'))
+
+hashpipe:write([[
+#include "nvim/arglist.h"
+#include "nvim/cmdexpand.h"
+#include "nvim/cmdhist.h"
+#include "nvim/digraph.h"
+#include "nvim/eval.h"
+#include "nvim/eval/buffer.h"
+#include "nvim/eval/deprecated.h"
+#include "nvim/eval/fs.h"
+#include "nvim/eval/funcs.h"
+#include "nvim/eval/typval.h"
+#include "nvim/eval/vars.h"
+#include "nvim/eval/window.h"
+#include "nvim/ex_docmd.h"
+#include "nvim/ex_getln.h"
+#include "nvim/fold.h"
+#include "nvim/getchar.h"
+#include "nvim/insexpand.h"
+#include "nvim/mapping.h"
+#include "nvim/match.h"
+#include "nvim/mbyte.h"
+#include "nvim/menu.h"
+#include "nvim/mouse.h"
+#include "nvim/move.h"
+#include "nvim/quickfix.h"
+#include "nvim/runtime.h"
+#include "nvim/search.h"
+#include "nvim/state.h"
+#include "nvim/strings.h"
+#include "nvim/sign.h"
+#include "nvim/testing.h"
+#include "nvim/undo.h"
+
+]])
+
+local funcs = require('nvim.eval').funcs
+for _, func in pairs(funcs) do
+  if func.float_func then
+    func.func = 'float_op_wrapper'
+    func.data = '{ .float_func = &' .. func.float_func .. ' }'
+  end
+end
+
+local metadata = mpack.decode(io.open(metadata_file, 'rb'):read('*all'))
+for _, fun in ipairs(metadata) do
+  if fun.eval then
+    funcs[fun.name] = {
+      args = #fun.parameters,
+      func = 'api_wrapper',
+      data = '{ .api_handler = &method_handlers[' .. fun.handler_id .. '] }',
+    }
+  end
+end
+
+local func_names = vim.tbl_filter(function(name)
+  return name:match('__%d*$') == nil
+end, vim.tbl_keys(funcs))
+
+table.sort(func_names)
+
+local funcsdata = assert(io.open(funcs_file, 'w'))
+funcsdata:write(mpack.encode(func_names))
+funcsdata:close()
+
+local neworder, hashfun = hashy.hashy_hash('find_internal_func', func_names, function(idx)
+  return 'functions[' .. idx .. '].name'
+end)
+
+hashpipe:write('static const EvalFuncDef functions[] = {\n')
+
+for _, name in ipairs(neworder) do
+  local def = funcs[name]
+  local args = def.args or 0
+  if type(args) == 'number' then
+    args = { args, args }
+  elseif #args == 1 then
+    args[2] = 'MAX_FUNC_ARGS'
+  end
+  local base = def.base or 'BASE_NONE'
+  local func = def.func or ('f_' .. name)
+  local data = def.data or '{ .null = NULL }'
+  local fast = def.fast and 'true' or 'false'
+  hashpipe:write(
+    ('  { "%s", %s, %s, %s, %s, &%s, %s },\n'):format(
+      name,
+      args[1],
+      args[2],
+      base,
+      fast,
+      func,
+      data
+    )
+  )
+end
+hashpipe:write('  { NULL, 0, 0, BASE_NONE, false, NULL, { .null = NULL } },\n')
+hashpipe:write('};\n\n')
+hashpipe:write(hashfun)
+hashpipe:close()