cleanup: fix badly dedented strings

[wchargin]

Summary:
Fixes #3034. These are artifacts of a global indentation change, which
didn’t touch strings because that changes the AST. In most cases, such
changes to the AST are fine, so we reindent the strings to be consistent
with their surroundings.

This diff is almost entirely whitespace.

Test Plan:
The following Python 3.8 script now only surfaces false positives:

import ast
import glob

def main():
    for filename in glob.glob("tensorboard/**/*.py", recursive=True):
        with open(filename) as infile:
            source = infile.read()
        sourcelines = source.splitlines()
        module = ast.parse(source, filename=filename)
        strings = [x for x in ast.walk(module) if isinstance(x, ast.Str)]
        for node in strings:
            base = _indent_of(sourcelines[node.lineno - 1])
            if node.lineno == node.end_lineno:
                # Rule out false positives on single-line strings with
                # literal "\n" escape sequences.
                continue
            lines = node.s.splitlines()
            if len(lines) <= 1:
                continue
            if any(_indent_of(x) < base for x in lines[1:] if x.strip()):
                print("%s:%d:%s" % (filename, node.lineno, _preview(lines)))

def _indent_of(line):
    n = 0
    for c in line:
        if c != " ":
            break
        n += 1
    return n

def _preview(lines):
    joined = " ".join(x.strip() for x in lines if x.strip())
    ellipsis = "..."
    maxlen = 40
    if len(joined) <= maxlen:
        return joined
    else:
        return joined[: maxlen - len(ellipsis)] + ellipsis

if __name__ == "__main__":
    main()

wchargin-branch: cleanup-string-indent

[nfelt]

Awesome, thanks for fixing this!