GLES2/3: error on declarations with unspecified precision

GLES2/3: error on declarations with unspecified precision

As specified:
  The fragment language has no default precision qualifier for floating
  point types. Hence for float, floating point vector and matrix
  variable declarations, either the declaration must include a precision
  qualifier or the default float precision must have been previously
  declared.
[GLSL ES 1.00 r17, section 4.5.3 (p36)]
[GLSL ES 3.00 r6, section 4.5.4 (p56)]
  Similarly, there is no default precision qualifier for the following
  sampler types in either the vertex or fragment language: (...)
[GLSL ES 3.00 r6, section 4.5.4 (p56)]

New tests:
  dEQP-GLES2.functional.shaders.declarations.unspecified_precision.*
  dEQP-GLES3.functional.shaders.declarations.unspecified_precision.*
Components: AOSP

Change-Id: Ic649556c73c83ba5f31125d25baf4c1c44fcf93f