Update to Vim to patchlevel 1439, change default python, improve vimrc

Some big changes in this update:

• Patchlevel 1439
• Default python is now 3.x instead of 2.x [1]
• Expose DEFAULT_VIMRC option (on by default) to vim-tiny

Also, many changes to the default vimrc. Any changes necessarily risk
contention, but then I remembered that I actually maintain editors/vim,
so here we are. The idea here is that Vim, by default, behaves like Vi,
and people who install the Vim port do so because they DON'T just want
Vi. I've enabled features that are basic quality-of-life settings for
me, and that I hope will be ideal for most end-users.

Important changes in the default vimrc:

• Don't install gvimrc at all. gvim should load $ETCDIR/vimrc anyway. I can't test gvim locally, so someone please let me know if I broke it.
• Turn on autoindent
• Disable console bells entirely. Console bells are terrible.
• Enable incsearch: highlights search results as you type them
• ^L clears search highlights while redrawing the screen
• Assume fast terminal by default
• Explain every setting in comments

Many of these settings are modeled after the defaults in NeoVim, which
really got it right. I want our default vimrc to be usable and ideal,
so please let me know if anything doesn't work for you, or if you have
other settings you'd like to see changed in the default.

In particular, please let me know if I broke gvim by removing the gvimrc!

PR: 235142 [1]
Submitted by: John W. O'Brien [1]