refactor!: rename vim.pretty_print => vim.print

Problem:
The function name `vim.pretty_print`:
1. is verbose, which partially defeats its purpose as sugar
2. does not draw from existing precedent or any sort of convention
   (except external projects like penlight or python?), which reduces
   discoverability, and degrades signaling about best practices.

Solution:
- Rename to `vim.print`.
- Change the behavior so that
  1. strings are printed without quotes
  2. each arg is printed on its own line
  3. tables are indented with 2 instead of 4 spaces
- Example:
  :lua ='a', 'b', 42, {a=3}
  a
  b
  42
  {
    a = 3
  }

Comparison of alternatives:
- `vim.print`:
  - pro: consistent with Lua's `print()`
  - pro: aligns with potential `nvim_print` API function which will
    replace nvim_echo, nvim_notify, etc.
  - con: behaves differently than Lua's `print()`, slightly misleading?
- `vim.echo`:
  - pro: `:echo` has similar "pretty print" behavior.
  - con: inconsistent with Lua idioms.
- `vim.p`:
  - pro: very short, fits with `vim.o`, etc.
  - con: not as discoverable as "echo"
  - con: less opportunity for `local p = vim.p` because of potential shadowing.

test/functional/lua/vim_spec.lua

@@ -6,6 +6,7 @@ local nvim_prog = helpers.nvim_prog
 local funcs = helpers.funcs
 local meths = helpers.meths
 local command = helpers.command
+local dedent = helpers.dedent
 local insert = helpers.insert
 local clear = helpers.clear
 local eq = helpers.eq
@@ -2269,7 +2270,7 @@ describe('lua stdlib', function()
 
   describe('vim.region', function()
     it('charwise', function()
-      insert(helpers.dedent( [[
+      insert(dedent( [[
       text tααt tααt text
       text tαxt txtα tex
       text tαxt tαxt
@@ -2923,6 +2924,24 @@ describe('lua stdlib', function()
       {4:-- Omni completion (^O^N^P) }{5:match 1 of 2}                    |
     ]]}
   end)
+
+  it('vim.print', function()
+    -- vim.print() returns its args.
+    eq({42, 'abc', { a = { b = 77 }}},
+      exec_lua[[return {vim.print(42, 'abc', { a = { b = 77 }})}]])
+
+    -- vim.print() pretty-prints the args.
+    eq(dedent[[
+
+      42
+      abc
+      {
+        a = {
+          b = 77
+        }
+      }]],
+      eval[[execute('lua vim.print(42, "abc", { a = { b = 77 }})')]])
+  end)
 end)
 
 describe('lua: builtin modules', function()