Revert pure virtual functions in UART component from #5920

[DrCoolzic]

What does this implement/fix?

PR5920 has introduced a braking change by adding two PURE virtual functions. Therefore ANY class derived from UARTComponent will not compile anymore !!! Big badaboom

This fix keeps the two new virtual functions introduced in PR5920 but not as PURE VIRTUAL functions.
What's amazing is that there was absolutely no reason to make them pure virtual ???

For more info see my comment on #5920

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Other

Related issue or feature (if applicable): fixes
#5920

Test Environment

• ESP32
• ESP32 IDF
• ESP8266
• RP2040
• BK72xx
• RTL87xx

Example entry for config.yaml:

NA

Checklist:

• The code change is tested and works locally.
• Tests have been added to verify that the new code works (under tests/ folder).

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in esphome-docs.

[probot-esphome]

Hey there @esphome/core, mind taking a look at this pull request as it has been labeled with an integration (uart) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[SeByDocKy]

Rework fine now with this PR thx :)

[edwardtfn]

Thanks for your prompt response to this, @DrCoolzic.

[DrCoolzic]

A big thank to @clyde @ssieb for helping me fix the commit history (went done from 148 to 1 :) )

[DrCoolzic]

Sorry for using incorrect terminology. It seems like breaking change has a specific meaning in esphome
see https://discord.com/channels/429907082951524364/429907082955718657/1185320271721271387 :

Apprently C++ breaking changes to a component API (e.g. https://www.cppdepend.com/detect-api-breaking-changes) is not considered as a breaking change for esphome. As I understand it, this term only applies if the yaml configuration is to be changed.

The interface change breaks the component I submitted 6 months ago, but as it hasn't been reviewed yet, it's still considered an external component.