minimal-printf: fix display decimals between -1 to 0 incorrect issue

[Linguanghsou]

Summary of changes

Fixes "minimal-printf doesn't display decimals between -1 to 0 correctly" listed in #13783

In original mbed_minimal_formatted_string_signed(), the type of augment value is a signed integer. Given a double value -0.00139 being printed, its integer part is 0 (-0 is equal to 0), so the condition "if (value < 0)" is false and it was handled as a positive decimal like 0.00139. In the fix, the value is a double type. Given a double value -0.00139, the condition "if (value < (double)0)" is true and it is handled as a negative decimal as expected.

Impact of changes

Migration actions required

Documentation

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Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

double d = -0.00139;
printf("d = %f\r\n",d);

--->
d = -0.001391

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[x] Tests / results supplied as part of this PR

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Reviewers

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[0xc0170]

We should continue with 13872. It does not have a test case yet.

I'll close this one.