Make = alignment in ABNF less chaotic

[glyn]

See https://github.com/ietf-wg-jsonpath/draft-ietf-jsonpath-base/issues/344#issuecomment-1410250684 and the following comments.

[cabo]

These are the length occurrences of the longer names:

17: 4
18: 2
19: 2
20: 3
21: 2
22: 1
23: 1

And these are those names:

- wildcard-selector
- function-argument
- abs-singular-path
- rel-singular-path
- function-name-char
- descendant-segment
- function-name-first
- bracketed-selection
- normal-index-segment
- normal-name-selector
- normal-single-quoted
- normal-index-selector
- member-name-shorthand
- singular-path-segments
- current-node-identifier

I'd try to align everything up to bracketed-selection.