Summary:
There are a lot of random training spaces on various lines. This patch
just got rid of all of them with `sed 's/\ \+$//g'.

Two major off-by-one errors are fixed in this patch. The first is in
float_to_string.h with length_for_num, which wasn't accounting for the
implicit leading bit when calculating the length of a number, causing
a missing digit on 80 bit float max. The other off-by-one is the
ryu_long_double_constants.h (a.k.a the Mega Table) not having any
entries for the last POW10_OFFSET in POW10_SPLIT. This was also found on
80 bit float max. Finally, the integer calculation mode was using a
slightly too short integer, again on 80 bit float max, not accounting
for the mantissa width. All of these are fixed in this patch.

This patch adds three options for printf decimal long doubles, and these
can also apply to doubles.

1. Use a giant table which is fast and accurate, but takes up ~5MB).
2. Use dyadic floats for approximations, which only gives ~50 digits of
   accuracy but is very fast.
3. Use large integers for approximations, which is accurate but very
   slow.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D150399

This is an ongoing series of commits that are reformatting our
Python code. This catches the last of the python files to
reformat. Since they where so few I bunched them together.

Reformatting is done with `black`.

If you end up having problems merging this commit because you
have made changes to a python file, the best way to handle that
is to run git checkout --ours <yourfile> and then reformat it
with black.

If you run into any problems, post to discourse about it and
we will try to help.

RFC Thread below:

https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style

Reviewed By: jhenderson, #libc, Mordante, sivachandra

Differential Revision: https://reviews.llvm.org/D150784

This change adds the High Precision Decimal described here:
https://nigeltao.github.io/blog/2020/parse-number-f64-simple.html
It will be used for the atof implementation later, but is complete and
tested now.

The code is inspired by the golang implmentation of the HPD class, which
can be found here: https://github.com/golang/go/blob/release-branch.go1.16/src/strconv/decimal.go

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D110454

Use expm1f(x) = exp(x) - 1 for |x| > ln(2).
For |x| <= ln(2), divide it into 3 subintervals: [-ln2, -1/8], [-1/8, 1/8], [1/8, ln2]
and use a degree-6 polynomial approximation generated by Sollya's fpminmax for each interval.
Errors < 1.5 ULPs when we use fma to evaluate the polynomials.

Differential Revision: https://reviews.llvm.org/D101134