feat: support float4 data type

[olavloite]

Adds support for the float4 / real data type.

Integration tests use float8 on environments that do not yet support float4.

[olavloite]

This is being removed now, as these are data types that needed special handling because:

1. We allow PostgreSQL clients to send us int2[], int4[] and float4[] arrays.
2. These are converted to int8[] and float8[] before being sent to Cloud Spanner.
3. This conversion is no longer needed for float4 when Cloud Spanner supports float4 natively.

[olavloite]

This is the 'typisdefined' column in pg_type. Up until now we listed float4 as a 'type that we know, but that is not implemented'.

[olavloite]

This change is not directly related to the addition of float4, but it popped up during the development that the error message was a bit weird. The error is thrown when the number of columns in the input of the COPY operation is different from the expected number of columns. The error message 'assumed' that the number of input columns was always smaller than the expected number of values (see the '... but only found' part).

[codecov]

Codecov Report

Attention: Patch coverage is 94.28571% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 90.79%. Comparing base (16eb184) to head (fbe73b1).
Report is 10 commits behind head on postgresql-dialect.

Files	Patch %	Lines
...e/cloud/spanner/pgadapter/parsers/FloatParser.java	83.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##             postgresql-dialect    #1481      +/-   ##
========================================================
+ Coverage                 90.72%   90.79%   +0.07%     
- Complexity                 2684     2701      +17     
========================================================
  Files                       144      144              
  Lines                      9226     9249      +23     
  Branches                   1342     1343       +1     
========================================================
+ Hits                       8370     8398      +28     
+ Misses                      578      574       -4     
+ Partials                    278      277       -1     

Flag	Coverage Δ
all_tests	90.79% <94.28%> (+0.07%)	⬆️

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[arawind]

LGTM, thanks!