fileset, revset: settle on optionally-quoted pattern syntax

Suppose revsets and filesets are primarily used in command shell, it would be
annoying if quoting is required in addition to the shell quoting. We might also
want to relax the revset parser to allow bare * in glob string.

Closes #2101

docs/revsets.md

···
 
 ## String patterns
 
-Functions that perform string matching support the following pattern syntax:
+Functions that perform string matching support the following pattern syntax (the
+quotes are optional):
 
-* `"string"`, or `string` (the quotes are optional), or `substring:"string"`:
-  Matches strings that contain `string`.
+* `"string"` or `substring:"string"`: Matches strings that contain `string`.
 * `exact:"string"`: Matches strings exactly equal to `string`.
 * `glob:"pattern"`: Matches strings with Unix-style shell [wildcard
   `pattern`](https://docs.rs/glob/latest/glob/struct.Pattern.html).

lib/src/fileset.pest

···
   | ""
 }
 
-// TODO: change rhs to string_literal to require quoting? #2101
 string_pattern = {
   strict_identifier
   ~ pattern_kind_op

lib/src/revset.pest

···
   | ""
 }
 
-// TODO: change rhs to string_literal to require quoting? #2101
 string_pattern = { strict_identifier ~ pattern_kind_op ~ symbol }
 
 primary = {