[SPARK-29888][SQL] new interval string parser shall handle numeric with only fractional part

[yaooqinn]

What changes were proposed in this pull request?

Current string to interval cast logic does not support i.e. cast('.111 second' as interval) which will fail in SIGN state and return null, actually, it is 00:00:00.111.

-- !query 63
select interval '.111 seconds'
-- !query 63 schema
struct<0.111 seconds:interval>
-- !query 63 output
0.111 seconds


-- !query 64
select cast('.111 seconds' as interval)
-- !query 64 schema
struct<CAST(.111 seconds AS INTERVAL):interval>
-- !query 64 output
NULL

Why are the changes needed?

bug fix.

Does this PR introduce any user-facing change?

no

How was this patch tested?

add ut

[yaooqinn]

cc @cloud-fan @MaxGekk, thanks in advance. this pr is raised via comment @ #26491 (comment)

[SparkQA]

Test build #113761 has finished for PR 26514 at commit 314829d.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #113760 has finished for PR 26514 at commit 74f8435.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[yaooqinn]

retest this please

[SparkQA]

Test build #113765 has finished for PR 26514 at commit 314829d.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #113792 has finished for PR 26514 at commit 76ba7ef.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[cloud-fan]

thanks, merging to master!

[yaooqinn]

thanks for merging