Fix regex for Examples for Scenario Outlines to match only correct tags.

[farost]

This PR fixes the issue with incorrect examples placeholders parsing, which does not, for example, let us using it in combination with some of the comparison operators (<, <=).

We change the matching pattern for these placeholders. Now it's the following:

1. First char should be alphanumeric: [A-Z | a-z | 0-9] (empty names are not supported)
2. Anything between the first and the last chars (if applicable) can be anything except of '<' and '>' so the placeholders are not confusing for both the users and the matcher. We don't provide escaping for such symbols, expecting that there should not be a need to use such symbols as part of a placeholder's name.
3. Last char should be alphanumeric: [A-Z | a-z | 0-9] (last char == first char for single-char namesj

[farost]

Some of the comments are taken into account and used in action. Some of the comments have just been replied to.