Adds luau.resolveConfig to @std

[tyulpan]

Adds luau.resolveConfig(filepath: path.Pathlike): LuauConfig to @std, which resolves the Luau configuration for a given file path by walking up the directory tree and merging .luaurc / .config.luau files.

Resolves #322.
Followed the official RFCs for .luaurc and the RFCs for .config.luau.

The dogfooding test suite passed, but it was excluded from the test file to avoid creating an unnecessary dependency:

suite:case("resolveConfigDogfooding", function(assert)
  local config = luau.resolveConfig(debug.info(1, "s"))
  assert.eq(config.languageMode, "strict")
  assert.neq(config.aliases, nil)
  assert.eq(config.aliases.batteries.value, "./batteries")
  assert.eq(config.aliases.std.value, "./lute/std/libs")
  assert.eq(config.aliases.lute.value, "./definitions")
  assert.eq(config.aliases.commands.value, "./lute/cli/commands")
end)