Re-implement ExprIdentifierVisitor::desc_expr to use Expr::Display

[andygrove]

Which issue does this PR close?

Part of #3330

Rationale for this change

Expr already implements the Display trait so it doesn't seem necessary for ExprIdentifierVisitor to have an alternate way to build descriptions of Expr.

The ExprIdentifierVisitor::desc_expr generated names are hard to interpret as well, IMO, so better to use the full description.

For example:

BEFORE: AggregateFunction-AVGfalseColumn-c
AFTER: AVG(#c)

What changes are included in this PR?

ExprIdentifierVisitor now just delegates to impl Display for Expr

Are there any user-facing changes?

Plans will look different

[andygrove]

@waynexia Does this look reasonable?

[waynexia]

Thanks for bringing this up. This Display way looks more pretty, I like it!

[ursabot]

Benchmark runs are scheduled for baseline = e26452a and contender = 786c319. 786c319 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java