Disallow abstract definitions from doctrine event listener registration
ISSUE #11300: Improve Routing Syntax Import Error

modified FileLoaderLoadException message to present the previous (Parse)Exception first
Add test and small code fix
Addition of the symfony license text
- Removed spaces around the concation dots to be more consitent
- adjusted some formatting
Merge remote-tracking branch 'upstream/master'
removed some more spaces
[Console] Skip commands from ConsoleCommandEvent

Use case: We have different variations of the same application, for which
only certain commands are allowed. Right now this is done in a custom
Application class, but it would be much easier to just be able to skip
commands from a listener, where you can disable commands via the Event
object.

This patch provides this feature and corresponding test cases.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes - for Console tests
| Fixed tickets | None
| License       | MIT
| Doc PR        | None
Changed order of validation
[Console][ProgressBar] Developer experience
 - Create getProgress/setProgress methods to replace getStep/setCurrent
 - ProgressBar::setCurrent should auto-start the ProgressBar.
 - You should be able to pass max to start
 - getStepWidth is internal information that should not be public
 - when verbosity set to quiet, the progress bar does not even need to
   execute all the logic to generate output that is then thrown away
[Console][ProgressBar] Allow to advance past max.
[Console][ProgressBar] Developer experience:
 - Removed barCharOriginal
 - getProgressPercent should return float instead of int.
 - Minor refactoring
[Translation] added method to expose collected messages
[YAML] resolve variables in inlined YAML
[Validator] deprecate member metadata accessors in favor of existing property metadata accessors

add changelog for deprecations

fix test
[Validator] add getConstraints to MetadataInterface
[Validator] fixed: Expressions always valid for null values

The ExpressionValidator was incorrectly skipping validation of null or
empty string values.
added useful reminder about form.vars.errors into UPGRADE-2.5 notes
minor #11619 added useful reminder about form.vars.errors into UPGRADE-2.5 notes (Oleg Andreyev)

This PR was submitted for the master branch but it was merged into the 2.5 branch instead (closes #11619).

Discussion
----------

added useful reminder about form.vars.errors into UPGRADE-2.5 notes

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

PR is just about upgrading UPGRADE-2.5 notes.
We've been upgrading from 2.4 to 2.5.3 and missing this part (upgrading templates)

Commits
-------

aefb1ca added useful reminder about form.vars.errors into UPGRADE-2.5 notes
Remove hard dependency of RequestContext in AssetsExtension