docs: rewrite binding-syntax section in template-syntax.md

[kapunahelewong]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Current section uses hero examples.

Issue Number:
Closes #18665

What is the new behavior?

Rewrite of Binding Section updates prose and introduces an example specific to Binding Syntax that demos the two examples that are currently explained in that section. It also moves away from heroes.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

This is part 2 of the Template Syntax rewrite. The intention is that each part be rewritten with relevant, separate examples. When the entire Template Syntax document is complete, these will be broken out into their own standalone docs.

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