TSVB: Cannot use large integers as static value

[cosmorogers]

Kibana version:
6.5.1

Elasticsearch version:
6.5.1

Server OS version:
CentOS 7

Browser version:
Firefox 60.2.1esr

Original install method (e.g. download page, yum, from source, etc.):
yum

Describe the bug:
Cannot use large integers as static value, eg 10737418240
Comes up with the error:
Invalid int constant [10737418240]. If you want a long constant then change it to [10737418240L].

However cannot enter the L as the Static Value field is type=number.
Using the browser developer tools to change the type to type=text is a hacky work around, you can then enter the L, and the static value displays correctly

Steps to reproduce:

1. Create new Time Series Visual Builder Visulalization
2. Change Aggregation to "Static Value"
3. Enter 10737418240 or other suitably large value
4. Observe error given back saying to use 10737418240L
5. Try and use "10737418240L"
6. Value is reset back to 0.

Expected behavior:
I can enter 10737418240L

Any additional context:
I am graphing the system.filesystem.available metric from metricbeat, and want to add a static value marker of 10GB so I can easily see if the available disk space left drops below 10GB.
10737418240 is 10gb in bytes.

[timroes]

Related to #1274

I will leave this open nevertheless, since it looks like we're giving a very specific help, that doesn't help, and maybe that can actually be fixed separate from the general support.

[elasticmachine]

Pinging @elastic/kibana-app